A method of a flash memory controller connected to a flash memory includes: receiving a data unit from the host via a bust of the host; controlling the flash memory to load a full page data from the flash memory into a buffer of the flash memory; and writing the data unit into the buffer to update or replace a portion data of the full page data stored in the buffer, to control the flash memory write the full page data which has been updated by the data unit from the buffer into the flash memory.