Abstract: On the moving base,a new initial alignment algorithm for strapdown inertial navigation system(SINS) is proposed.In this algorithm,two special inertial frames,the initial-time inertial frame(i₀ frame) and the initial-time SINS body inertial frame(i_b0 frame),are defined and are selected as transition reference frames.The calculation of initial alignment direction cosine matrix(DCM) between SINS body frame(b frame) and navigation reference frame(n frame) is expanded into three parts:(1) the DCM between i₀ frame and n frame is easily obtained via local geographical coordinates and initial alignment time;(2) by expressing SINS specific force equation in b frame and by the aid of external velocity log,the constant DCM from i_b0 frame to i₀ frame is achieved;(3) attitude updating using gyro samples gets the DCM between b frame and i_b0 frame.In the end,some vehicular tests are carried out on the moving base and the accuracy of azimuth reaches about 0.1°(1σ).