In order to achieve fast initial alignment of Strap-down Initial Navigation System (SINS) with gyros information under circumstance of disturbance and strong noise,Quasi-Equality Constrained Kalman Filter (QECKF) was introduced,based on which the model of SINS initial alignment was established.According to the characteristics of the SINS onboard land vehicles,it was proposed to use IIR low-pass filter at first for noise reduction,then the filtering method of QECKF together with KF.The scheme made full use of the gyro information,and could realize fast initial alignment.Result of the test under disturbance of engine and operators showed that the speed of the algorithm was increased by 25% compared with the normal KF.The algorithm solved the problem of estimation divergence of the normal method.