In order to reduce the impacts of atmospheric turbulence and background light etc. factors to atmospheric laser communication system performance, the atmospheric laser communication system using circular polarization modulation technology is adopted and researched. This system uses polarization shift keying modulation (PloSK), which is a new standard digital modulation technique in optical communication field. In this modulation, two rotation states of the circle polarization light (left handed and right handed) representation logic signal ' 0 ' and ' 1 ', are used to information loaded and data transmission. In the receiver, the modulation optical signal is detected with dual differential probe method. Under the OptiSystem system simulation environment, several direct detection system model based on OOK intensity modulation, single rode circular polarization modulation and circular polarization modulation with balanced detection is constructed, and compares and analysis of the various communication system performance. The results show that: at the same parameter conditions, bit error rate of CPolSK system with balanced detection lower about two orders of magnitude than the OOK system and single rode CPolSK system, the eye diagram and the waveform chart are also significantly better than OOK system’s. It can be seen, based on circular polarization shift keying (CPolSK) laser communication system with dual differential detection is superior on anti-interference of atmospheric interference, and reducing error rate, and will be easy to implement.