A data storage device including a flash memory and a controller. The flash memory includes a plurality of blocks, and each of the blocks has a plurality of pages. The controller receives a write command which is arranged to write a plurality of data sectors into a plurality of first pages of a first block of the blocks, calculates an offset index according to a first erase count of the first block, retrieving a plurality of seeds from a random seed table according to the offset index, encodes the data sectors by using the retrieved seeds to obtain a plurality of encoded data sectors, and writes the encoded data sectors into the first pages.