Abstract: In order to quickly determine reasonable lidar ratiothe key parameter in the inversion of lidar geometric form factor,a simple and convenient method was presented to determine the lidar ratio for the geometrical form factor is a constant as 1 in lidar full zone. This method is theoretically deduced and verified with actual lidar data. The retrieved geometric form factor does not appear increasing or decreasing monotonously in full zone,which shows that this method is reasonable and effective,avoiding a large of qualitative analysis which is tedious and time consuming. It is useful to get lidar geometric form factor and obtain the surface aerosol important information.