The present invention discloses a method for accessing a flash memory module, wherein the flash memory module comprises a plurality of block, each block is implemented by a plurality of word lines, and each word line comprises a plurality of memory cells supporting a plurality of states. The method comprises the steps of: reading the memory cells of at least a first word line of a specific block of the plurality of blocks to obtain a cumulative distribution information of the states of the memory cells; determining a target decoding flow selected from at least a first decoding flow and a second decoding flow according to the cumulative distribution information; reading the memory cells of a second word line to obtain readout information of the second word line; and using the target decoding flow to decode the readout information of the second word line.