Abstract: The relation between ratio of parallel and perpendicular polarization components of the airborne lidar’s polarized backscatted signals and crystal thickness are analyzed quantitatively using plane parallel plate pattern and crystal membranous theory when the polarized lights permeate 1/2 retardation sheet. Optimal processing thickness and appropriate processing thickness ranges of 1/2 quartz retardation sheet and 1/2 calcite retardation sheet for measurement of airborne lidar polarization gain ratio values are analyzed quantitatively and discussed. At the same time, unfitted processing thickness ranges are pointed out. There are some differences between gain ratios measured respectively when the polarized direction of return signal is parallel or perpendicular with the optical axis of