Abstract: Aiming at the initial alignment requirement of strapdown inertial navigation system(SINS) under linear moving disturbance environment while the vessel is moored, an initial alignment method with bothprecision and rapidity is proposed based on an improved parameter identification model. In the traditional parameter identification model, the first order approximation of the sinusoidal and cosine functions for the earth angular velocity will cause the initial alignment result to diverge over time. Therefore, the first order approximation of the sinusoidal and cosine functions is replaced by the high order approximation to reduce the modeling error. At the same time, the influence of linear moving disturbance on the velocity error observation is taken into consideration, and the constant estimation term is added into the parameter identification model to reduce the influence and to improve the alignment accuracy. Digital simulations and actual alignment tests are performed under different conditions. The results show that under the linear moving disturbance test for the given IMU(inertial measurement unit) device, the alignment accuracy of the horizontal attitude and the heading is respectively 20 arc‐second and 4 arcmin.