In order to test the high dynamic performance of the on-orbit star sensor and develop better software for motion compensation, a simulation algorithm of blurred star image is proposed. First, the projection position of the guide star on the star sensor image plan is calculated by the pinhole model. And considering the motion blurred of the star image because of the carrier motion, the image motion velocity model is build. Second, based on the angular distance of the star sensor bore-sight, searching guided star in the field of view. Third, the gray-scale of the star image is simulated from the image motion velocity model by adding noises. The simulation tests show that the proposed method has better computation speed and precision.