In order to satisfy the requirement of rapid alignment in moorage and consider the limitation of analytic
alignment based on navigation coordinate, the analytic alignment based on inertial coordinate is proposed. According to
the characteristics that the earth rate is constant and the gravitational acceleration presents the coning motion in the inertial
coordinate, IIR digital filter is used to filter the interference angular velocity and acceleration of vehicle. The gyroscope
output which is filtered by low-pass digital filter, is smoothed based on the average algorithm by weighting. By using the
information of the earth rate and gravitational acceleration which are filtered by low-pass digital filter, and the projection
of them on the navigation coordinate, the attitude matrix is established. Simulation results show that, the precision of the
analytic initial alignment achieves the medium navigation accuracy requirement.