Airborne 3-D focal imaging LiDAR can take images in a very short gating time (3~5ns), so it can shield background noise instantaneously. Since the area of laser irradiated surface is about when the detected distance is about 3km, to ensure high imaging quality the laser beam needs to be smoothed before it arrives the ground. In this paper, based on self-developed airborne 3-D focal imaging LiDAR system, a beam homogenization device by using lens array method is presented for the detection range from 1km to 3km. The experimental result indicates that the smoothing rate can reach 89%. Subsequent tests in LiDAR system show that the homogenization device is reliable and effective.