Abstract: There is a badly influence of the existence of ring laser gyro’s random walk on the performance of ring laser gyro strapdown inertial navigation system(SINS). In order to quantitatively study the influence of ring laser gyro’s random walk on SINS,an error formula is derived with a mathematical method. Simulation has been done according to the given flight trajectory and the given factor of ring laser gyro’s random walk.The simulation results are analyzed.