Gain ratio calibration error is one of the most significant factors affecting the accuracy of a polarization lidar depolarization ratio. This paper analyzes the basic principles of various existing gain ratio calibration methods and compares the advantages and disadvantages of the+ 45 method,±45 method,∆ 45 method, rotation fitting method and pseudo-depolarizer method in practice though experiments. Results show that: the∆ 45 method,±45 method and rotation fitting method are relatively accurate when the misalignment angle is small, but the operation of the±45 method and rotation fitting method are more complicated. The+ 45 method still has a large calibration error without a misalignment angle. The pseudo-depolarizer method is the easiest to operate, but it is restricted by a non-ideal pseudo-depolarizer. Through comparison of theory and experiment, this paper provides a suggestion for the best choice of gain ratio calibration method. It is recommended that the±45 method be used for calibration with a half-wave plate, and the pseudo-depolarizer method be used for calibration with a high-precision depolarizer.