The lidar geometric factor describes the overlap between the laser beam and the receiver of field of view in differential absorption lidar. It is an important system parameter in differential absorption lidar. An experimental determination method of the lidar geometric factor is presented based on the comparison of aerosol scattering ratio profile derived from the signals measured by differential absorption lidar and Mie lidar simultaneously. The approach provides a means to determine the lidar geometric factor without an explicit knowledge of all lidar system parameter, such as the telescope diameter, laser beam divergence, telescope of field of view et al. The application of the proposed method can reduce the ozone measurement error of differential absorption liar and improve the potential of differential absorption lidar to investigate the spatial and temporal distribution characteristics of ozone.