With the consideration of the intensity scintillation caused by the atmosphere turbulence in the downlink of the ground-to-satellite optical communication system, BER performances of three different modulation schemes OOK, 2PSK, QPSK are explored and compared. Simulation results are given and conclusions are achieved through the discussions of the advantages and disadvantages of various schemes, which may cause contributions to the selection of the modulation format in the design of the ground-to-satellite laser communication system.