For its better spectral response characterization, higher quantum efficiency and signal-to-noise ratio, camera is more and more used in atmospheric parameters measurement lidar. Camera lidars retrieval atmospheric parameters by analyzing the light column images acquired by the cameras and objectives through gathering the backscatter light of the laser beam. Lidars of this kind usually have higher spatial resolution and better real time performance. However, because of its limited depth of field (DOF), the measurement accuracy of the area out of the DOF is influenced by optical defocus in different degree. In the meantime, it is also not suitable for portable equipments for using small relative aperture receiving objective. Based on improving the design of the receiving objective, a new design scheme is proposed in this paper about improving the optical receiving system of the camera lidar. This scheme can improve the measurement accuracy of the area out of the DOF in traditional structure by using large DOF, large relative aperture offaxis objective and the special using mode of the camera. The optical receiving system designed according to this scheme is more compact and is especially suitable for portable instrument. Furthermore, the relation among the focus length, the distance between laser and objective and the installation angle is also analyzed in this paper. The formula is given at the same time. This scheme is carried out in camera lidar system in laboratory and the results are satisfactory.