The asymmetrically clipped optical orthogonal frequency division multiplexing (OFDM) modulation technique is investigated. It is a new technique for using OFDM in optical system. Asymmetrically clipped OFDM is derived from a bipolar OFDM waveform by setting the negative values to zero. The asymmetrically clipped OFDM technique is applied to atmospheric communication system in this paper, and the performance of atmospheric communication system using asymmetrically clipped OFDM technique through atmospheric turbulence channels is analyzed. On this basis, the low density parity check (LDPC) codes and belief propagation (BP) iterative decoding algorithm are applied into the atmospheric communication system, and it is simulated in the atmospheric turbulence channel with combination of asymmetrically clipped optical OFDM intensity modulation. The simulation results show that LDPC codes have excellent error correction capabilities and access to a larger coding gain,and the above scheme can satisfy the need of atmospheric laser communication system.