The present invention provides a method for accessing a flash memory module, wherein the method comprises: building a physical block recording table corresponding to a logical address to physical address (L2P) mapping table, wherein the physical block recording table records at least one block whose physical address is recorded in the L2P mapping table; and when a specific block within the flash memory module is under a garbage collection operation, for a data page of the specific block whose logical address is within the L2P mapping table, referring to the physical block recording table to determine if reading the L2P mapping table from the flash memory module or not, for determining the data page to be valid or invalid.