A method is proposed to aid in the comparison of spaceborne lidar measurements with ground-based lidar measurements. The downward attenuated backscatter is constructed from ground-based lidar data, and then compared to the attenuated backscatter measured by spaceborne lidar. To test the accuracy of the method, sensitivity analysis is performed. This method is applied to compare the measurements between the CALIPSO lidar and ground-based lidar at Hampton University. The comparison results show this method is a feasible and reasonable approach for spaceborne lidar validation. Moreover, it can help to retrieve aerosol optical properties.