A method used in a flash memory module having a plurality of storage blocks is disclosed. Each storage block can be used as a first block or a second block wherein a cell of the first block is arranged for storing data of 1 bit and a cell of the second block is arranged for storing data of at least 2 bits. The method includes: classifying data to be programmed into a plurality of groups of data; executing error code encoding to generate a corresponding parity check code to store the groups of data and the corresponding parity check code to at least one block of first blocks; and after completing storing the groups of data, performing an internal copy operation upon the groups of data and the corresponding parity check code from the at least one block of the first blocks to at least one second block.