A new compensation method is proposed to solve the problem that the positioning errors of ring laser gyro inertial navigation system diverge when the warship has sailed for a long time. Classical error equation and single-axis rotary ring laser gyro error equation are introduced, the effects of gyro drift of INS are analyzed, then based on the analysis results, a compensation method depend on external position Information and heading Information is presented. Theoretical analysis and test results show that the compensation method could effectively restrain the system errors and greatly improve the SINS navigation accuracy in long-endurance applications.