The light intensity control system and the cavity length control system are used in the design of the laser gyro. Transfer functions of the light intensity control system of prism laser gyros are established based on the theory of the control system. The equivalent mathematical model of the ring laser in the light intensity control system is established by experiments and tests. Based on theoretical analysis and Matlab simulation, performance of the laser gyro light intensity control system can be evaluated accurately. It offers theoretic base for system design and improves performance of the laser gyro and debugging efficiency.