Optical signal would be distorted during transmission in fiber caused by dispersion,and the non-ideal optical amplification would also lead t o error bits.In order to restrain the effects,in this paper,quasi-cyclic low density parity check (QC-LDPC) codes are studied i n a 40Gbit/s non-return-to-zero differential phase shift lceying (NRZ-DPSK) signal transmission system based on fiber-based optical parametric amplificati on (FOPA) so that the performance of the optical communication system could be improved.The results indicate that under 10km fib er length,the bit error rate (BER) can achieve 10 －11 because of the QC-LDPC codes with the same code length but different cod e rates,and then the different fiber lengths are tested for the same QC-LDPC co des,the BER can achieve 10－11 also.QC-LDPC codes constructed by the maximization of the shortest cycle algori thm can correct the bits errors caused by dispersion,nonlinearity,and pump jitter,and consequently the co mmunication quality can be improved.