In the resonant optical gyro, the stability of light intensity is crucial for obtaining good dynamic and static performance characteristics. In this work, the effects of the laser intensity fluctuation on the scale factor nonlinearity and Kerr effect error were studied by combined experimental and theoretical analysis. Then, a simple light intensity feedback loop was designed using an intensity modulator, and the light intensity was calibrated in real time using the maximum value of the second harmonic demodulation curve. Experimental results show that the fluctuations of the light intensity entering the gyro system are reduced by about two orders of magnitude through the use of the light intensity feedback loop. The system scale factor nonlinear error was decreased from 13.74% to 2.79% and the dynamic performance of the gyroscope was improved. Additionally, the long-term (1 h) bias stability of 16.94  deg  /  h was obtained.