The present invention provides a method for access a flash memory module, wherein the method includes the steps of: sending a read command to the flash memory module to read a plurality of memory cells of at least one word line of the flash memory module by using a plurality of read voltages, wherein each memory cell is configured to store a plurality of bits, each memory cell has a plurality of states, the states are used to indicate different combinations of the plurality of bits; obtaining readout information from the flash memory module; analyzing the readout information to determine numbers of the states of the memory cells; determining if the memory cells are balance or unbalance according the numbers of the states of the memory cells to generate a determination result; and referring to the determination result to adjust voltage levels of the plurality of read voltages.