A data backup method for a flash memory module is provided. The flash memory module includes a plurality of flash memory units. In the data backup method, a controller is first provided to receive a backup function enabling signal. The controller then configures the flash memory units according to the backup function enabling signal such that at least one of the flash memory units is configured as a backup storage area and the flash memory units that are not in the backup storage area are configured as a main storage area. The controller then checks and receives an updated status of important data in the main storage area and backs up the important data into the backup storage area according to the updated status. Accessing to the backup storage area and accessing to the main storage area by the controller are independent.