Abstract: The analysis of random walk coefficient is very important to the overall performance evaluation of fiber optic gyro (FOG). Two methods were introduced to analyze FOG random walk noise, Allan variance and modified Allan variance. Static data were used to calculate the noise contents in fiber optic gyroscope (FOG)s output with these two methods, and the results were compared. The final results show that modified Allan variance can distinguish all types of noise easily with increased computation time and the computation accuracy of the various FOG random walk noise coefficients can be improved.