In order to analyze the influence of sky background light on a space laser communication system and provide corresponding reference data for total design of communication links at the same time, a sky background light noise model is established and analyzed theoretically. Simulation results show that the sky background light causes the decrease of signal to noise ratio of the detector used in the coarse and fine tracking units, and then leads to the decrease of tracking precision and the increase of bit error rate of the communication system. According to the performance index of the system, the influence of sky background light on the system performance is effectively reduced to meet the requirements of the mission of the communication link when we choose the communication wavelength properly, use an optical system with minor-caliber and narrow bandwidth, and select the optimal zenith angle and communication time.