diff --git a/source/module_base/module_mixing/mixing_data.cpp b/source/module_base/module_mixing/mixing_data.cpp
index 6c41757ee3..27d3292a72 100644
--- a/source/module_base/module_mixing/mixing_data.cpp
+++ b/source/module_base/module_mixing/mixing_data.cpp
@@ -3,7 +3,7 @@
 namespace Base_Mixing
 {
 
-Mixing_Data::Mixing_Data(const int& ndim, const int& length, const size_t& type_size)
+Mixing_Data::Mixing_Data(const int& ndim, const std::size_t& length, const size_t& type_size)
 {
     this->ndim_tot = ndim;
     this->length = length;
@@ -15,16 +15,18 @@ Mixing_Data::Mixing_Data(const int& ndim, const int& length, const size_t& type_
 
 Mixing_Data::~Mixing_Data()
 {
-    if (this->data != nullptr)
+    if (this->data != nullptr) {
         free(this->data);
 }
+}
 
-void Mixing_Data::resize(const int& ndim, const int& length, const size_t& type_size)
+void Mixing_Data::resize(const int& ndim, const std::size_t& length, const size_t& type_size)
 {
     this->ndim_tot = ndim;
     this->length = length;
-    if (this->data != nullptr)
+    if (this->data != nullptr) {
         free(this->data);
+}
     if (ndim * length > 0)
     {
         this->data = malloc(ndim * length * type_size);
diff --git a/source/module_base/module_mixing/mixing_data.h b/source/module_base/module_mixing/mixing_data.h
index 69c2629c65..e5986f7faa 100644
--- a/source/module_base/module_mixing/mixing_data.h
+++ b/source/module_base/module_mixing/mixing_data.h
@@ -22,7 +22,7 @@ class Mixing_Data
      * @param type_size size of type
      *
      */
-    Mixing_Data(const int& ndim, const int& length, const size_t& type_size);
+    Mixing_Data(const int& ndim, const std::size_t& length, const size_t& type_size);
 
     /**
      * @brief Destroy the Mixing_Data object
@@ -38,7 +38,7 @@ class Mixing_Data
      * @param type_size size of type
      *
      */
-    void resize(const int& ndim, const int& length, const size_t& type_size);
+    void resize(const int& ndim, const std::size_t& length, const size_t& type_size);
 
     /**
      * @brief push data to the tensor
@@ -54,7 +54,7 @@ class Mixing_Data
 #ifdef _OPENMP
 #pragma omp parallel for schedule(static, 4096/sizeof(FPTYPE))
 #endif
-        for (int i = 0; i < length; ++i)
+        for (std::size_t i = 0; i < length; ++i)
         {
             FP_startdata[i] = data_in[i];
         }
@@ -86,7 +86,7 @@ class Mixing_Data
     // the number of vectors for mixing
     int ndim_tot = 0;
     // the length of each vector
-    int length = 0;
+    std::size_t length = 0;
     // the start index for vector: start = this->index_move(0)
     int start = -1;
     // the number of used vectors for mixing
diff --git a/source/module_base/module_mixing/pulay_mixing.cpp b/source/module_base/module_mixing/pulay_mixing.cpp
index e3ad3b3f70..9c9c10a7bd 100644
--- a/source/module_base/module_mixing/pulay_mixing.cpp
+++ b/source/module_base/module_mixing/pulay_mixing.cpp
@@ -28,13 +28,13 @@ void Pulay_Mixing::tem_push_data(Mixing_Data& mdata,
                                  std::function<void(FPTYPE*, const FPTYPE*, const FPTYPE*)> mix,
                                  const bool& need_calcoef)
 {
-    const size_t length = mdata.length;
+    const std::size_t length = mdata.length;
     std::vector<FPTYPE> F_tmp(length);
 
 #ifdef _OPENMP
 #pragma omp parallel for schedule(static, 4096 / sizeof(FPTYPE))
 #endif
-    for (int i = 0; i < length; ++i)
+    for (std::size_t i = 0; i < length; ++i)
     {
         F_tmp[i] = data_out[i] - data_in[i];
     }
@@ -69,7 +69,7 @@ void Pulay_Mixing::tem_push_data(Mixing_Data& mdata,
 #ifdef _OPENMP
 #pragma omp parallel for schedule(static, 4096 / sizeof(FPTYPE))
 #endif
-        for (int i = 0; i < length; ++i)
+        for (std::size_t i = 0; i < length; ++i)
         {
             FP_F[i] = F_tmp[i];
         }
@@ -81,7 +81,7 @@ void Pulay_Mixing::tem_push_data(Mixing_Data& mdata,
 #ifdef _OPENMP
 #pragma omp parallel for schedule(static, 4096 / sizeof(FPTYPE))
 #endif
-        for (int i = 0; i < length; ++i)
+        for (std::size_t i = 0; i < length; ++i)
         {
             FP_startF[i] = F_tmp[i];
         }
@@ -103,7 +103,7 @@ void Pulay_Mixing::tem_cal_coef(const Mixing_Data& mdata, std::function<double(F
         ModuleBase::WARNING_QUIT(
             "Pulay_mixing",
             "One Pulay_Mixing object can only bind one Mixing_Data object to calculate coefficients");
-    const int length = mdata.length;
+    const std::size_t length = mdata.length;
     FPTYPE* FP_F = static_cast<FPTYPE*>(F);
 
     if (mdata.ndim_use > 1)