The codeword accessing method including: receiving a write data with M message bits; generating parity information with N-M bits based on an error correction algorithm and the M message bits, where N and M are positive integers; transforming the M message bits and the parity information to a scrambled codeword with N bits by a scrambling operation, where the scrambled codeword contains only a part of the M message bits; and writing the scrambled codeword into a memory device.