The sensitivity of the ring laser gyroscope based on the Sagnac principle increases with the size of the gyroscope increasing, which is directly connected to the earth and can accurately monitor the earth's rotation angular velocity. And it has wide applications such as universal time precision measurement, seismic wave detection, geodesy and basic physics. The size of the geodesic laser gyroscope is often larger for the sensitivity increasing with the size of the gyroscope increasing. However, as the size increasing, the free spectral range of the cavity becomes smaller, and it becomes difficult to obtain a single longitudinal mode. Laser gyroscope often works in the fundamental mode. Aiming at the problem of laser gyroscope mode, the experimental results of the first active geodesic laser gyroscope in China is reported. The pipe diaphragm is used to achieve single transverse mode, and the critical gain method makes the laser gyroscope single longitudinal mode operation become possible. Through the light intensity feedback control, the stability of the laser gyroscope signal is improved, which helps to accurately measure the angular velocity of the earth's rotation.