Abstract: A method of independent initial alignment of a marine strapdown inertial navigation system in moorage is studied to arm at the problems which are brought by a base swinging with large angles and centripetal-acceleration disturbance on the base. Parameter identification is used to pick-up the several coefficients in attitude error expressions in order to identify gyro bias and attitude error. Moreover, an idea that compensates in real time acceleration disturbance on a swing base is addressed. Finally, simulation calculations are given to show the validity of the method.