On the basis of error propagation characteristics of an Inertial Navigation System(INS) and the effect of axial Ring Laser Gyroscope(RLG) on the errors of longitude and latitude, a calibrating method for the RLG drift was proposed to solve the problems that single-axis rotation could compensate the vertical RLG errors automatically, but could not compensate the axial RLG errors in a single-axis rotation INS. First, the auto-compensation principle of the single-axis rotation INS was introduced briefly. Then, the effect of the axial RLG drift, initial heading and attitude error, and initial velocity error on the longitude and the latitude was analyzed on the stationary base. Depending on the errors of longitude and latitude, a new method based on the least squares was proposed to calibrate the RLD drift precisely. Finally, the static and vehicle navigation experiments were performed. The results show that the identification precision reaches 0.000 5 (°)/h and radial position error of the INS is less than 1 nm/72 h. The axial RLG drift can be calibrated precisely by the least square method proposed and the experiment result of navigation meets practical demands.