Abstract: To study the fast initial alignment of ring laser gyro (RLG) strapdown inertial navigation system for land vehicle, the two-position alignment technology was adopted, the principle and software flow of the method were presented, the alignment precision was tested and the error sources having influence on alignment precision were analyzed. The influences of gyro constant drift and accelerometer bias on alignment precision are eliminated by the two-position alignment method. Moreover the three gyros constant drifts and three acce1erometers biases were calibrated at alignment and compensated in the navigation state, so the navigation precision was improved effectively.