Laser illumination is an effective technology for the imaging and tracking to the far dim targets in the air. Because of laser transmitting in the air, the spatial distribution of intensity on the target plane is non-uniform caused by atmospheric turbulence, and the laser wavefront generates aberration, which decreases image resolution and tracking accuracy in optical system. A model of illumination laser propagation in atmosphere has been built. Under the condition of moderate turbulence, weak turbulence and multi-beams, numeric simulation for laser illumination to air targets has been carried out, and the affects of illumination light intensity and wavefront on remote target imaging are analyzed. The results show that illumination light intensity fluctuation variance below 0.5 and wavefront aberration standard error below 0.2 λ meet 1 μrad magnitude resolution capability.