Abstract: In order to study the influence of different curvatures on the performance parameters of ring laser gyro (RLG), the diffractive loss calculation model was established in theory based on the cavity theory. The waist variation of RLG resulted from the curvature variation assembly was calculated by simulation, which could further cause diffraction loss variation. And starting from the effect of aperture diffractive loss on the backscattering of RLG，the influence of waist on the performance of RLG was analyzed. The calculated results indicates that the variation of diffractive loss is 3% when the variation of the curvature radius is less than 0.3 m, which would cause the bias varying 0.013 Hz; the variation of diffractive loss is 15% when the variation of the curvature radius is about 0.6 m, which would cause the bias varying 0.021 Hz; thus, the variation of diffractive exceeds to 30% when the variation of the curvature radius is more than 1.5 m, which would cause the resonator detuning, that is no laser comes into being. Both loss and bias were measured when the curvature was changed. The test results accords with the theory, the variation of curvature has obviously effect on diffractive loss and its performance.