Abstract: An algorithm of complexity reduction of list decoding is given by using side information. Then in-depth analysis the reasons of complexity reduction and side information based on shift register sequence is provided. Compared with the method of using stable channel transmission side information, it does not use additional channel, and also not affect the decoding performance and complexity, more easy to engineering realization. Finally, the traditional ordered statistic decoding algorithm is improved by using a small amount of the most reliable bits as side information, thus the decoding list is significantly reduced.