Secondary quick alignment method of marine strapdown inertial navigation system

The invention provides a secondary quick alignment method of a marine strapdown inertial navigation system. The method comprises the following steps: continuously collecting output data of an optical fiber gyro and a quartz flexible accelerometer after preheating the system, and processing the collected data to finish the rough alignment of the strapdown inertial navigation system; performing primary fine alignment after the rough alignment, creating an error equation of the marine strapdown inertial navigation system, performing Kalman filtering by using a speed error as observed quantity so as to obtain an estimated value of a misalignment angle, and compensating the ship body posture; and expanding the residual misalignment angle to a new state variable by using the compensated posture as a reference posture on the basis of the primary fine alignment, and further aligning the levelness and the direction through using a speed and misalignment angle error matching method. The method disclosed by the invention can be used for accurately estimating zero offset of a horizontal accelerometer on the condition of ensuring the alignment precision and quickness.