The invention provides a memory device. The memory device includes a flash memory, a memory, and a controller. The flash memory includes a plurality of blocks for data storage. The memory stores an address mapping table recording relationships between logical addresses and physical addresses of the blocks therein. The controller divides the address mapping table stored in the memory to a plurality of mapping table units, updates relationships between the logical addresses and the physical addresses stored in the mapping table units, determines whether data access performed to the flash memory fulfills the conditions of a specific requirement, and when the data access fulfills the conditions of the specific requirement, the controller selects a target mapping table unit from the mapping table units, and stores the target mapping table unit and a corresponding time stamp as a mapping table unit data to the flash memory.