Abstract: This paper presents an alignment method of strapdown INS in a swaying vehicle which conbines the least square estimation method with the real-time updating to an astitute matrix. The given algorithm is simulated in various swaying conditions and compared, with the classical gyrocompassing approach The simulation results indicate that this method effectively improves the alignment performance, and the alignment time of azimuth is shortened by 50% as compared with that iu the gyrocompassing approachin the same simulation conditions. ...