In this paper, we analyze the performance of LDPC decoder for DVB-S2 system. The performance analysis is performed by computer simulations based on AWGN channel and high order modulation technique including 16APSK and 32APSK. For normal frame codeword length N=64800, the performance of LDPC decoder is only away 0.7dB to dB from Shannon limit with respect to each modulation. The constructions and encoding process of LDPC codes which are used for DVB-S2 system are also presented and described.