Methods and devices capable of erasing a flash memory evenly are provided, in which a flash memory comprises a data region with a plurality of data blocks and a spare region with a plurality of spare blocks, and a controller retrieves a corresponding data with a check code from a first data block of the flash memory according to a read command from a host, performs a predetermined check to the corresponding data by the check code, determines whether an error is correctable when a check result of the predetermined check represents that the error has occurred, and increases an erase count of the first data block by a predetermined value when the error is correctable.