A novel construction method of quasi-cyclic low-density parity-Ccheck(QC-LDPC) codes is proposed.A sufficient condition of the construction approach for QC-LDPC codes without girth-four is presented.Considering the characteristics of optical communication systems,a QC-LDPC(4 221,3 956) code for high-speed long-haul optical communication system,based on the proposed method is constructed.The analysis of the simulation result shows that the net coding gain(NCG) of the QC-LDPC(4 221,3 956) code is 1.8 dB and 0.2 dB more than that of the classic RS(255,239) code and SCG-LDPC(3 969,3 720) code respectively at code rate of 93.7% and BER of 10-6.And at the same condition,the NCG of the QC-LDPC(4 221,3 956) code is about 1.4 dB away from the Shannon limit.Furthermore,the error floor of QC-LDPC(4 221,3 956) code is far lower than that of the PEG-LDPC(4 221,3 956) code,which just meets the requirement of optical communication systems.