In order to reduce the influence of atmospheric turbulence on the performance of atmospheric optical communication system, low-density parity-check (LDPC) codes combined with multiple-input multiple-output technologies is applied. Decoding initialization formulas of single-input multiple-output (SIMO) system are derived in the forms of maximal ratio combining (MRC), equal gain combining (EGC) and selection combining, the system bit-error-rate (BER) performances are compared. The simulation results show that the atmospheric optical communication SIMO system of LDPC coding has better BER performance than that in SISO system; error performance of SIMO system differs with different combining schemes; the system in MRC has the lowest bit error rate followed by system in EGC with the same signal-to-noise ratio; with the increasing number of receiving antennas in a certain number of transmitting antennas, the BER will be decreased. So, it has some significance in the design of atmospheric optical communication system and theoretical research.