Abstract: Large disturbance is introduced into fiber optic gyroscope under vibration environment. And the error characteristics for FOG are severely affected with the ability of tracking disturbance as the existence of non-linear factors, which becomes more complicated as the result of the additional feedback delay. Therefore, it is important for solving vibration problem to analyze the feedback delay. Firstly, impacts on the closed-loop tracking ability and the stability against disturbance of FOG with different feedback delay were analyzed with the non-linear factors. Then, the non-linear element was considered based on the linear control model, and the outputs of FOG with different feedback delay were obtained and the tracking performance was analyzed by simulation as keeping the same stability margin. The simulation and final experiment show that the bias of FOG will be brought into a large offset under vibration with a poor tracking performance. Thus, it is important to solve the vibration problem of FOG by improving the closed-loop tracking ability with a small feedback delay.