diff --git a/docs/sphinx_doc/source/tutorial/trinity_configs.md b/docs/sphinx_doc/source/tutorial/trinity_configs.md
index 0c858ae505..19dda755bd 100644
--- a/docs/sphinx_doc/source/tutorial/trinity_configs.md
+++ b/docs/sphinx_doc/source/tutorial/trinity_configs.md
@@ -475,6 +475,7 @@ trainer:
   use_dynamic_bsz: true
   max_token_len_per_gpu: 16384
   ulysses_sequence_parallel_size: 1
+  max_checkpoints_to_keep: 5
   trainer_config: null
 ```
 
@@ -499,6 +500,7 @@ trainer:
 - `use_dynamic_bsz`: Whether to use dynamic batch size.
 - `max_token_len_per_gpu`:  The maximum number of tokens to be processed in forward and backward when updating the policy. Effective when `use_dynamic_bsz=true`.
 - `ulysses_sequence_parallel_size`: Sequence parallel size.
+- `max_checkpoints_to_keep`: Maximum number of checkpoints to keep. Older checkpoints will be deleted. If not specified, all checkpoints will be kept.
 - `trainer_config`: The trainer configuration provided inline.
 ---
 
diff --git a/docs/sphinx_doc/source_zh/tutorial/trinity_configs.md b/docs/sphinx_doc/source_zh/tutorial/trinity_configs.md
index 6d96bff547..d130517920 100644
--- a/docs/sphinx_doc/source_zh/tutorial/trinity_configs.md
+++ b/docs/sphinx_doc/source_zh/tutorial/trinity_configs.md
@@ -472,6 +472,7 @@ trainer:
   use_dynamic_bsz: true
   max_token_len_per_gpu: 16384
   ulysses_sequence_parallel_size: 1
+  max_checkpoints_to_keep: 5
   trainer_config: null
 ```
 
@@ -496,6 +497,7 @@ trainer:
 - `use_dynamic_bsz`: 是否使用动态批量大小。
 - `max_token_len_per_gpu`: 训练过程中，每个 GPU 最大 token 长度; 当 `use_dynamic_bsz=true` 时生效。
 - `ulysses_sequence_parallel_size`: 序列并行的并行度，即用于分割单个序列的 GPU 数量。
+- `max_checkpoints_to_keep`: 保留的最大检查点数量。超过此数量后，最旧的检查点将被删除。如果未指定，则将保留所有检查点。
 - `trainer_config`: 内联提供的 trainer 配置。
 
 ---
diff --git a/tests/trainer/trainer_test.py b/tests/trainer/trainer_test.py
index 3cd4c8f856..136d95c366 100644
--- a/tests/trainer/trainer_test.py
+++ b/tests/trainer/trainer_test.py
@@ -344,6 +344,10 @@ def test_trainer(self, mock_load):
 
         # sft warmup stage
         sft_config = stage_configs[0]
+        self.assertEqual(
+            sft_config.synchronizer.sync_interval,
+            sft_config.trainer.save_interval,
+        )
         parser = TensorBoardParser(os.path.join(sft_config.monitor.cache_dir, "tensorboard"))
         rollout_metrics = parser.metric_list("rollout")
         self.assertEqual(len(rollout_metrics), 0)
@@ -374,11 +378,15 @@ def test_trainer(self, mock_load):
         self.assertEqual(parser.metric_min_step(response_metrics[0]), 1)
         self.assertEqual(parser.metric_max_step(response_metrics[0]), 4)
         # test save checkpoint when sft finish
+        for i in range(3):
+            self.assertFalse(
+                os.path.exists(os.path.join(sft_config.checkpoint_job_dir, f"global_step_{i}"))
+            )
         self.assertEqual(
             get_checkpoint_dir_with_step_num(
-                checkpoint_root_path=sft_config.checkpoint_job_dir, trainer_type="verl", step_num=2
+                checkpoint_root_path=sft_config.checkpoint_job_dir, trainer_type="verl", step_num=3
             )[1],
-            2,
+            3,
         )
         # test save checkpoint at last step
         checkpoint_dir, step_num = get_checkpoint_dir_with_step_num(
@@ -749,7 +757,7 @@ def setUp(self):
         if multiprocessing.get_start_method(allow_none=True) != "spawn":
             multiprocessing.set_start_method("spawn", force=True)
         self.config = get_template_config()
-        self.config.buffer.total_epochs = 1
+        self.config.buffer.total_steps = 6
         self.config.buffer.batch_size = 4
         self.config.model.model_path = get_model_path()
         self.config.explorer.rollout_model.engine_type = "vllm_async"
@@ -762,21 +770,20 @@ def setUp(self):
         self.config.synchronizer.sync_method = SyncMethod.CHECKPOINT
         self.config.explorer.eval_interval = 4
         self.config.buffer.explorer_input.taskset = get_unittest_dataset_config("countdown")
-        self.config.trainer.save_interval = 4
+        self.config.trainer.save_interval = 2
         self.config.trainer.save_hf_checkpoint = "last"
         self.config.trainer.trainer_strategy = self.strategy
+        self.config.trainer.max_checkpoints_to_keep = 2
         self.config.check_and_update()
         self.process_list = []
 
-    def test_trainer(self):
+    def test_trainer(self):  # noqa: C901
         """Test the checkpoint saving."""
         _trainer_config = self.config.trainer.trainer_config
         if self.strategy == "megatron":
             _trainer_config.actor_rollout_ref.actor.megatron.tensor_model_parallel_size = 2
             _trainer_config.actor_rollout_ref.ref.megatron.tensor_model_parallel_size = 2
             _trainer_config.critic.megatron.tensor_model_parallel_size = 2
-        _trainer_config.trainer.max_actor_ckpt_to_keep = 2
-        _trainer_config.trainer.max_critic_ckpt_to_keep = 2
 
         stop_event = multiprocessing.Event()
         trainer_process = multiprocessing.Process(target=run_both, args=(self.config, stop_event))
@@ -839,6 +846,10 @@ def test_trainer(self):
                 # print(f"State dict check at {state_dict_iteration} iteration passed.")  # for debug
 
             if checkpoint_iteration > 0:
+                flag_file = os.path.join(
+                    default_local_dir, f"global_step_{checkpoint_iteration}", ".full_checkpoint"
+                )
+                self.assertTrue(os.path.exists(flag_file))
                 for sub_dir_name in ["critic", "actor"]:
                     iteration_dir = os.path.join(
                         default_local_dir, f"global_step_{checkpoint_iteration}", sub_dir_name
@@ -882,6 +893,28 @@ def test_trainer(self):
                 # print(f"Checkpoint check at {checkpoint_iteration} iteration passed.")  # for debug
         if not stop_event.is_set():
             self.fail("Training process failed to stop.")
+        # check only full checkpoint dirs are kept
+        for sync_step in [1, 3, 5]:
+            state_dict_dir = os.path.join(default_local_dir, f"global_step_{sync_step}")
+            self.assertFalse(
+                os.path.exists(state_dict_dir),
+                f"Found unexpected state dict dir at step {sync_step}",
+            )
+        for checkpoint_step in [4, 6]:
+            checkpoint_dir = os.path.join(default_local_dir, f"global_step_{checkpoint_step}")
+            self.assertTrue(
+                os.path.exists(checkpoint_dir),
+                f"Missing expected checkpoint dir at step {checkpoint_step}",
+            )
+            actor_checkpoint_dir = os.path.join(checkpoint_dir, "actor")
+            self.assertTrue(os.path.exists(actor_checkpoint_dir))
+        # check step 2 should have no checkpoint
+        checkpoint_dir = os.path.join(default_local_dir, "global_step_2")
+        self.assertTrue(os.path.exists(checkpoint_dir))
+        actor_checkpoint_dir = os.path.join(checkpoint_dir, "actor")
+        self.assertFalse(os.path.exists(actor_checkpoint_dir))
+        critic_checkpoint_dir = os.path.join(checkpoint_dir, "critic")
+        self.assertFalse(os.path.exists(critic_checkpoint_dir))
         trainer_process.join(timeout=10)
         self.assertIn("model.safetensors", huggingface_dir_files)
 
diff --git a/trinity/algorithm/algorithm.py b/trinity/algorithm/algorithm.py
index ebe5978a07..5206d3c513 100644
--- a/trinity/algorithm/algorithm.py
+++ b/trinity/algorithm/algorithm.py
@@ -63,6 +63,27 @@ def default_config(cls) -> Dict:
             "entropy_loss_fn": "none",
         }
 
+    @classmethod
+    def check_config(cls, config: Config) -> None:
+        if config.mode == "train":
+            if (
+                config.buffer.trainer_input.experience_buffer is None
+                or not config.buffer.trainer_input.experience_buffer.path
+            ):
+                raise ValueError(
+                    "`buffer.trainer_input.experience_buffer.path` is required when `algorithm.algorithm_type == sft`"
+                )
+        elif config.mode in ["both", "explore"]:
+            raise ValueError(f"SFT does not support `{config.mode}` mode")
+
+        if config.synchronizer.sync_method != SyncMethod.CHECKPOINT:
+            config.synchronizer.sync_method = SyncMethod.CHECKPOINT
+            logger.warning(
+                "SFT only supports checkpoint synchronization, set `synchronizer.sync_method` to `checkpoint`."
+            )
+
+        config.synchronizer.sync_interval = config.trainer.save_interval
+
 
 class PPOAlgorithm(AlgorithmType):
     """PPO Algorithm."""
@@ -232,6 +253,7 @@ def check_config(cls, config: Config) -> None:
             logger.warning(
                 "DPO only supports checkpoint synchronization, set `synchronizer.sync_method` to `checkpoint`."
             )
+        config.synchronizer.sync_interval = config.trainer.save_interval
         if config.algorithm.repeat_times != 2:
             config.algorithm.repeat_times = 2  # Fake repeat times
         if config.algorithm.kl_loss_fn in {"none", None}:
diff --git a/trinity/common/config.py b/trinity/common/config.py
index c80d84b61e..d7e8e3a059 100644
--- a/trinity/common/config.py
+++ b/trinity/common/config.py
@@ -735,6 +735,7 @@ class TrainerConfig:
     # TODO: extract more train-related params from underlying trainer engine
 
     save_strategy: SaveStrategy = SaveStrategy.UNRESTRICTED
+    max_checkpoints_to_keep: Optional[int] = None
 
     trainer_config: Any = field(default_factory=dict)
     trainer_config_path: str = ""  # deprecated, use `trainer_config` instead
diff --git a/trinity/common/models/utils.py b/trinity/common/models/utils.py
index 445f1f63ba..5e3b9f1020 100644
--- a/trinity/common/models/utils.py
+++ b/trinity/common/models/utils.py
@@ -199,6 +199,10 @@ def load_state_dict(checkpoint_dir: str, config: TrainerConfig) -> Union[dict, T
     Args:
         checkpoint_dir (str): The checkpoint directory.
         trainer_type (str): The trainer type. Only support "verl" for now.
+
+    Returns:
+        Union[dict, Tuple[str, str]]: The state dict. If the checkpoint uses
+            megatron dist checkpointing, return a tuple of (method, checkpoint_dir).
     """
     if config.trainer_type == "verl":
         strategy = config.trainer_strategy
diff --git a/trinity/common/models/vllm_worker.py b/trinity/common/models/vllm_worker.py
index 15220b18dc..e84f2c1746 100644
--- a/trinity/common/models/vllm_worker.py
+++ b/trinity/common/models/vllm_worker.py
@@ -68,6 +68,7 @@ def update_weight(self):
         if self._weight_update_rank == 0:
             state_dict, model_version = ray.get(self.synchronizer.get_model_state_dict.remote())
             if isinstance(state_dict, tuple):
+                # currently only megatron return a tuple
                 method, checkpoint_dir = state_dict
                 if method == "megatron":
                     if self._checkpoint_converter is None:
diff --git a/trinity/common/verl_config.py b/trinity/common/verl_config.py
index 5db971245d..96e9d7f524 100644
--- a/trinity/common/verl_config.py
+++ b/trinity/common/verl_config.py
@@ -413,6 +413,9 @@ def synchronize_config(self, config: Config) -> None:  # noqa: C901
         self.trainer.group_name = config.group
         self.trainer.experiment_name = config.name
         self.trainer.default_local_dir = config.checkpoint_job_dir
+        if config.trainer.max_checkpoints_to_keep is not None:
+            self.trainer.max_actor_ckpt_to_keep = config.trainer.max_checkpoints_to_keep
+            self.trainer.max_critic_ckpt_to_keep = config.trainer.max_checkpoints_to_keep
         if not config.continue_from_checkpoint:
             self.trainer.resume_mode = "disable"
         else:
diff --git a/trinity/manager/synchronizer.py b/trinity/manager/synchronizer.py
index c0b913812e..9b7cfd414e 100644
--- a/trinity/manager/synchronizer.py
+++ b/trinity/manager/synchronizer.py
@@ -2,6 +2,7 @@
 
 import asyncio
 import os
+import shutil
 from collections import defaultdict
 from typing import Dict, List, Optional, Tuple, Union
 
@@ -95,13 +96,14 @@ async def _find_verl_latest_state_dict(self) -> None:
         )
         while True:
             if os.path.exists(local_latest_state_dict_iteration):
+                current_model_version = self.model_version
                 try:
                     with open(local_latest_state_dict_iteration, "r") as f:
                         latest_model_version = int(f.read().strip())
                 except (IOError, ValueError) as e:
                     self.logger.warning(f"Failed to read or parse state dict iteration file: {e}")
                     continue
-                if latest_model_version > self.model_version:
+                if latest_model_version > current_model_version:
                     self.logger.info(
                         f"Synchronizer has found a new model state dict at step {latest_model_version}."
                     )
@@ -119,8 +121,22 @@ async def _find_verl_latest_state_dict(self) -> None:
                         f"Synchronizer has loaded model state dict from checkpoint {latest_model_version}."
                     )
                     await self.set_model_state_dict(model_state_dict, latest_model_version)
+                    # remove the previous checkpoints to save disk space
+                    await self._remove_previous_state_dict(current_model_version)
             await asyncio.sleep(1)
 
+    async def _remove_previous_state_dict(self, previous_model_version: int) -> None:
+        previous_state_dict_dir = os.path.join(
+            self.config.checkpoint_job_dir, f"global_step_{previous_model_version}"
+        )
+        if os.path.exists(previous_state_dict_dir):
+            # check if it's a full checkpoint, only remove checkpoints for sync
+            if not os.path.exists(os.path.join(previous_state_dict_dir, ".full_checkpoint")):
+                self.logger.info(
+                    f"Removing previous checkpoint for sync at step {previous_model_version}."
+                )
+                shutil.rmtree(previous_state_dict_dir, ignore_errors=True)
+
     async def _find_tinker_latest_state_dict(self) -> None:
         default_local_dir = self.config.checkpoint_job_dir
         local_latest_state_dict_iteration = os.path.join(
@@ -320,9 +336,7 @@ async def get_latest_model_version(self) -> int:
         async with self._ready_condition:
             return self.model_version
 
-    async def ready_to_nccl_sync(
-        self, module: str, trainer_step: Optional[int] = None
-    ) -> Union[int, None]:
+    async def ready_to_nccl_sync(self, module: str, trainer_step: int) -> Union[int, None]:
         """
         Prepare for NCCL-based synchronization between modules.
 
@@ -330,7 +344,7 @@ async def ready_to_nccl_sync(
 
         Args:
             module: Either 'trainer' or 'explorer'.
-            trainer_step: Optional step number from the trainer.
+            trainer_step: Step number from the trainer.
 
         Returns:
             The model version if both sides are ready; otherwise None.
diff --git a/trinity/trainer/tinker_trainer.py b/trinity/trainer/tinker_trainer.py
index e355630063..1265348491 100644
--- a/trinity/trainer/tinker_trainer.py
+++ b/trinity/trainer/tinker_trainer.py
@@ -282,6 +282,15 @@ def save_checkpoint(self, block_until_saved: bool = False, save_as_hf: bool = Fa
             f"global_step_{self.train_step_num}",
         )
         os.makedirs(local_path, exist_ok=True)
+
+        # save a flag to indicate this is a full checkpoint dir
+        # make sure this flag is created before notifying the synchronizer
+        # to avoid the synchronizer recognizing it as a state_dict-only checkpoint
+        # TODO: use a better way to indicate full checkpoint
+        flag_path = os.path.join(local_path, ".full_checkpoint")
+        with open(flag_path, "w") as f:
+            f.write("")
+
         remote_checkpoint_path = os.path.join(local_path, "remote_checkpoint_path.txt")
         with open(remote_checkpoint_path, "w") as f:
             f.write(self.latest_remote_checkpoint_path)
diff --git a/trinity/trainer/verl/fsdp_checkpoint_manager.py b/trinity/trainer/verl/fsdp_checkpoint_manager.py
index 4c3a6aba57..38391bd679 100644
--- a/trinity/trainer/verl/fsdp_checkpoint_manager.py
+++ b/trinity/trainer/verl/fsdp_checkpoint_manager.py
@@ -48,6 +48,7 @@
 
 from trinity.manager.synchronizer import Synchronizer
 from trinity.trainer.verl_trainer import CheckpointMonitor
+from trinity.utils.log import get_logger
 
 
 class FSDPCheckpointManager(OldFSDPCheckpointManager):
@@ -62,6 +63,7 @@ class FSDPCheckpointManager(OldFSDPCheckpointManager):
 
     def __init__(self, *args, ray_namespace: str = "", **kwargs):
         super().__init__(*args, **kwargs)
+        self.logger = get_logger()
         self.synchronizer = Synchronizer.get_actor(namespace=ray_namespace)
         self.checkpoint_monitor = CheckpointMonitor.get_actor(
             namespace=ray_namespace,
@@ -439,6 +441,10 @@ def save_checkpoint(
             and local_path != self.previous_saved_paths[-1]  # type: ignore
         ):  # last step may save twice
             keep_start = len(self.previous_saved_paths) - max_ckpt_to_keep + 1  # type: ignore
+            self.logger.info(
+                "Checkpoint manager is removing previous checkpoints at "
+                + str(self.previous_saved_paths[:keep_start])  # type: ignore
+            )
             self.remove_previous_save_local_path(self.previous_saved_paths[:keep_start])  # type: ignore
             self.previous_saved_paths = self.previous_saved_paths[keep_start:]  # type: ignore
 
diff --git a/trinity/trainer/verl/megatron_checkpoint_manager.py b/trinity/trainer/verl/megatron_checkpoint_manager.py
index 4fadcae477..6659975307 100644
--- a/trinity/trainer/verl/megatron_checkpoint_manager.py
+++ b/trinity/trainer/verl/megatron_checkpoint_manager.py
@@ -40,6 +40,7 @@
 
 from trinity.manager.synchronizer import Synchronizer
 from trinity.trainer.verl_trainer import CheckpointMonitor
+from trinity.utils.log import get_logger
 
 
 class MegatronCheckpointManager(OldMegatronCheckpointManager):
@@ -59,6 +60,7 @@ def __init__(
             *args,
             **kwargs,
         )
+        self.logger = get_logger()
         self.synchronizer = Synchronizer.get_actor(namespace=ray_namespace)
         self.checkpoint_monitor = CheckpointMonitor.get_actor(
             namespace=ray_namespace,
@@ -340,6 +342,10 @@ def save_checkpoint(
             and local_path != self.previous_saved_paths[-1]  # type: ignore
         ):  # last step may save twice
             keep_start = len(self.previous_saved_paths) - max_ckpt_to_keep + 1  # type: ignore
+            self.logger.info(
+                "Checkpoint manager is removing previous checkpoints at "
+                + str(self.previous_saved_paths[:keep_start])  # type: ignore
+            )
             self.remove_previous_save_local_path(self.previous_saved_paths[:keep_start])  # type: ignore
             self.previous_saved_paths = self.previous_saved_paths[keep_start:]  # type: ignore
 
diff --git a/trinity/trainer/verl_trainer.py b/trinity/trainer/verl_trainer.py
index 8583fd3363..e5870e8e3b 100644
--- a/trinity/trainer/verl_trainer.py
+++ b/trinity/trainer/verl_trainer.py
@@ -494,6 +494,15 @@ def _save_checkpoint(self, save_as_hf: bool = False):
             self.config.trainer.default_local_dir, f"global_step_{self.global_steps}"
         )
 
+        # save a flag to indicate this is a full checkpoint dir
+        # make sure this flag is created before notifying the synchronizer
+        # to avoid the synchronizer recognizing it as a state_dict-only checkpoint
+        # TODO: use a better way to indicate full checkpoint
+        os.makedirs(local_global_step_folder, exist_ok=True)
+        flag_path = os.path.join(local_global_step_folder, ".full_checkpoint")
+        with open(flag_path, "w") as f:
+            f.write("")
+
         self.logger.info(f"local_global_step_folder: {local_global_step_folder}")
         actor_local_path = os.path.join(local_global_step_folder, "actor")