Refresh control method for memory system to perform refresh action on all memory banks of the memory system within refresh window

A refresh control method for a memory controller of a memory system is provided. The memory controller is connected with a memory. The memory includes plural memory banks. The refresh control method includes the following steps. Firstly, a refresh state of the memory device is read, and thus a refresh window is realized. Then, a refresh command is issued to the memory device according to the refresh state. The refresh command contains a memory bank number field and a memory bank count field. The memory bank count field indicates a first count. The first count of memory banks are selected from the plural memory banks of the memory device according to the memory bank number field and the first count. Moreover, a refresh operation is performed on the first count of memory banks.