Disclosed is a memory system and a method of programming a multi-bit flash memory device which includes memory cells configured to store multi-bit data, where the method includes and the system is configured for determining whether data to be stored in a selected memory cell is an LSB data; and if data to be stored in a selected memory cell is not an LSB data, backing up lower data stored in the selected memory cell to a backup memory block of the multi-bit flash memory device.