Beginning with the theoretical model of lock-in of ring laser gyro, through the study of the relationship between the lock-in, backscatter and beam intensity, the characteristic of the lock-in signal contained in the laser beam signal is analyzed. The filtering circuit and signal extraction algorithm are designed. Through the precise control of sampling time, multiple order filtering and coordinate transform tracking, lock-in signal is extracted from beam intensity signal and controlled. It is important to take measures to suppress integrated backscatter and give full play to the performance of optical devices. It can decrease the bias drift on long time and improve the bias stability of gyro.