The scale factor of large laser gyroscope has a strong dependence on the geometric deformation of the ring cavity. According to the structure and working characteristics of the large laser gyroscope, the key technologies affecting the measurement accuracy are studied, and the geometric deformation of the ring cavity which affects the scaling factor is calculated and analyzed. The variation of the scaling factor after the geometric deformation of the ring cavity is obtained. In addition, the optimization method of the scale factor of the ring cavity is presented, and the variation of temperature and stress on the scale factor is given. It is concluded that when the production conditions, working environments and cavity structures are same, the compensation of scale factor is beneficial to the improvement of measuring accuracy of large laser gyroscope.