In view of the negative effects of resonant cavity deformation due to complex environments on performance of laser gyroscope, the slight deformations of mirror in three directions, which are 0.342 5″, 0.349 4″ and 0.215 0″, was simulated by ANSYS when the resonant cavity was under the function of standard random vibration spectrum(gRMS=6.6 g). Employing the theory of matrix optics, the deformation of the diaphragm was obtained quantitatively. Then, the deformation law of optical resonant cavity affected by radius of curvature, cavity length and incident angle was analyzed in an optical quadrangular cavity. Finally, the deformation law of optical path was derived when the spherical mirror and spherical mirror changed simultaneously or the spherical mirror and plane mirror changed simultaneously. Only considering the vibration resistance, the deformation of quadrangular cavity generated by the external environment is slighter with the smaller radius of curvature and the shorter cavity length when the radius of curvature ranges from 0 to 8 m and cavity length ranges from 0 to 1 m. Furthermore, the deformation law of two mirrors can be equivalent to that of a single mirror according to certain rules. The research can provide a reference for the design of optical resonant cavity of laser gyroscope.