Memory device and method of operating

The invention provides a memory device and an operation method thereof. The memory device comprises a controller, a memory and a flash memory. The operation method comprises the following steps of: dividing an address mapping table memorized in the memory into a plurality of mapping sub-tables; updating the correspondence relations of logical addresses and physical addresses of the flash memory recorded in the mapping sub-tables; checking whether the access motion of the controller on the flash memory meets a first specified condition; every time the access motion of the controller on the flash memory meets the first specified condition, sequentially selecting a current mapping sub-table from the mapping sub-tables, and recording the current mapping sub-table and a corresponding time stamp serving as mapping sub-table data in the flash memory. After sudden power failure, the memory device can reestablish the latest address mapping table before the power failure, reduce the consumption of the writing bandwidth of the flash memory, and reduce the starting time of a system.