The gain characteristics of laser gyro were investigated by measuring the relative strength of the laser gyro′s side spectrum. It was obtained experimentally that the gain of the laser gyro increases with the increasing of the current, the gyro gain presents the saturated gain phenomena with the increasing of the total pressure and the gain reaches a maximum value when the total pressure is about equal to 4P0. By comparing the timevarying gain curves of aluminum cathode and B cathode gyroscope in the gyro′s startup phase and corrying out error analysis of experimental data, the experimental results show that the gain stability and antienvironmental interference capability of B cathode gyro are better than that of aluminum cathode gyro. The gain of active medium and the beat′s frequency shift induced by the Langmuir flow effects both are related to the population density difference of the producing laser′s upper and lower level. The experimental results show that the zero drift′s stability of the laser gyro can be evaluated by the gyro gain′s stability.