Low-density parity check code(LDPC)is a good approximation of the Shannon limit. It has decoding with low complexity and flexible structure. It was the hot-spot of channel coding field in recent years so that it has the widespread application prospect in the optical communication system. In the view of LDPC long code based on irregular Tanner graph which has good performance and its application in the optical communication system, this paper constructed several LDPC codes,and used BP algorithm to carry out computer simulation in the AWGN channel and under the BPSK modulation. According to the BER and the FER curve of regular and irregular LDPC code, not only coding and decoding but also performance are analyzed and compared.At last, the paper makes some suggestion as to the LDPC code with the practical value in the optical communication system. Through the theoretical analysis and simulation results show that the LDPC code has a good performance, and can save hardware costs so that it is suitable in optical communication system and can be used as a super-forward error correction candidate code.