A method of programming a NAND flash memory device includes providing a flash memory device, wherein word lines are disposed between a drain selecting line and a source selecting line, wherein a first word line is provided adjacent to the source selecting line and a last word line is provided adjacent to the drain selecting line; and selecting a word line to program memory cells coupled to the selected word line to perform an even LSB program operation and an odd LSB program operation for the selected first word line. Each of the word lines is selected until all of the word lines have been selected, so that the even LSB program operation and the odd LSB program operation can be performed for all of the word lines. The even LSB program operation is performed to store a lower rank data bit in memory cells coupled to an even bit line assigned a selected word line. The odd LSB program operation is performed to store a lower rank data bit in memory cells coupled to an odd bit line assigned to the selected word line.