A method for writing data into a flash memory, wherein the flash memory includes a plurality multi-level cells, and each of the plurality of multi-level cells is capable of storing a plurality of bits. The method includes: storing a first bit into each of the plurality of multi-level cells respectively; determining if each of the plurality of multi-level cells stores the first bit respectively; and when each of the plurality of multi-level cells stores the first bit respectively, storing a second bit into each of the plurality of multi-level cells respectively.