The refractive indexes of prisms are affected by temperature, hence the optical characteristics of triangular prisms ring cavity is disturbed enough to affect the stability of the laser gyro. Considering the temperature perturbation, the transmission matrices of the reflected and refracted beams on the prism surfaces have been modified. The modified results are the old 2×2 beam transfer matrices are corrected to new 3×3 matrices and the temperature perturbations are added. According to the self-consistent theory of the laser ring cavity, a physical model of the ring cavity light transmission with the temperature disturbance has been established. The theoretical analysis shows that when the temperature varies from -40℃ to 70℃, the changes of the optical cavity-length, frequency offset, and scale factor are 49μm, 0.011MHz and 1.96×10-10, respectively. An experimental system of the prism laser gyroscope has been established whose temperature can be changed, and the experimental results agree with the theoretical values.