Abstract: Optical dither is introduced to improve lock-in for better performance of laser gyro. The influence of the back-scatter light on the lock-in of laser gyro was investigated, and the basic principle of back-scatter reduction and lock-in improvement with optical dither was expounded. Optical path variation under optical dithering was carried out by perturbation and the best theoretical amplitude of optical dither for lock-in was deduced. The experiments were done according to the concept. The result showed that the effect of optical dither was similar to mechanically dithered noise, which could improve the bias stability of gyro. Therefore, optical dither is suitable for laser gyro to improve the lock-in.