Aiming at the difficulty of realizing the independent coarse alignment of the vessel strapdown inertial navigation system (SINS) on the moving base, the process of coarse alignment for vessel SINS on moving base is studied. A method to achieve coarse alignment of vessel SINS by global position system (GPS) is proposed. The strapdown attitude matrix is calculated by integrating the basic equations of SINS with the position information obtained by GPS. Compared with the coarse alignment achieved by external velocity measurement, the proposed method realizes coarse alignment with the position information obtained by GPS, and does not need to be equipped with Doppler velocity log. Therefore, the method is less expensive and more practicable. Finally, simulations have been conducted and results show that coarse alignment of SINS during voyages can be accomplished rapidly, with errors of attitude angles less than 1°, which is obviously suitable for accuracy requirement for the subsequent fine alignment.