Abstract: In order to predict and estimate the effects of atmospheric turbulence, vibration of terminals and misalignment on space laser communication, the amplitude of detected signals changing with lateral offset (between the center of the focused beam and the center of the photodetector in the detecting plane and defocus (between the detecting plane and the focal plane, are calculated in simulation and measured in experiment, and the fit error rate (BER), signal-to-noise ratio and jitter of the detected signals changing with lateral offset and defocus are also measured. The results show that the performance of space laser communication systems would deteriorate significantly as the lateral offset and defocus increase, and the lateral offset has more effect. The maximum defocus and lateral offset