When free space optical communication system uses the atmosphere as a medium for information transmission, received signals are inevitably influenced by the atmospheric environment, atmospheric turbulence, background light factors, and so on. Considering that the atmosphere channel has a great influence on the laser atmosphere communication quality, a modulation/demodulation technology based on polarization parameters is proposed, and an atmospheric laser communication system based on polarization shift keying (PolSK) is designed. This system uses polarization shift keying modulation. In this modulation, two rotation states of circle polarization (left and right) are used for information transmission. In the receiver, the optical signal is detected with balance detection method. At the same time, the performance of the system is simulated. The results show that the modulation/demodulation techniques based on polarization parameters have unique advantages, such as anti-atmospheric interference, high data rate and low bit error rate. It will have broad prospects for development and application in future space laser communication.