Can i delete some files?

[gugongerguo]

about 104GB,can i delete this file?

[gugongerguo]

another question , why my db file named *_mainnet.sqlite, but the database_path = db/blockchain_v1_CHALLENGE.sqlite in config.yaml?

[loppefaaret]

Cause the CHALLENGE will get resolved to whatever "network" you are farming on - if "mainnet", the file will inherit that in the filename - if "testnet10", it would inherit that in its filename
and no, you cannot delete this file, if you run a node (which has a copy of the entire blockchain, and that is what the file is)
what i can recommend, is that you upgrade to 1.3.X, and look into upgrading your database from "v1" to "v2" - this will save you about 45% space for that database file.
Read more about it here:
https://github.com/Chia-Network/chia-blockchain/wiki/CLI-Commands-Reference#db