Abstract: In order to predict and estimate the effects of the atmosphere turbulence on airborne laser communication system, the second-order statistics of transmitted beam are deduced and calculated, which include beam diameter, beam wander, spatial coherence radius and the angle of arrival. The results show that the effects of atmosphere turbulence on airborne laser communication will be mitigated significantly as the altitude of airborne platform increases. Due to the larger atmosphere refractive index structure constant in lower altitude, the beam diameter and beam wander in uplink are larger than those in downlink. The angle of arrival in downlink is on the order of several rad, which is larger than that in uplink. Based on the methods and the results, the effects caused by atmosphere turbulence on airborne laser communication systems can be predicted and estimated accurately.