As the star sensor works under high dynamic conditions, the spot formed by the star on the imaging plane will become a tail, which directly reduces the accuracy of centroid positioning. In addition, the imaging quality of the star sensor is seriously hit by the rolling shutter effect in the rolling shutter exposure mode, which further increases positioning error. Considering the diffusion radius and the dynamic tailing of the star spot, the imaging trajectory and the energy distribution models of the star spot under the rolling shutter exposure mode are established in this paper. Furthermore, based on the purposed models, the influence of the starting positions of stars and the dispersion of star spots to the centroid positioning error are analyzed by numerical simulation respectively, from which the variation laws of the two kinds of errors are obtained. Then, the laboratory experiments are implemented to evaluate the latter error; it indicates from the experimental results that the variation of the latter error is consistent with the simulation results, which is simultaneously proved that it cannot be ignored in practical engineering application. These results can be a valuable reference for developing a high precision star sensor. The models proposed in this paper can describe the star imaging process and evaluate the centroid positioning accuracy under the roller shutter exposure mode effectively, which lays a foundation for further eliminating the rolling shutter effect in the following research and improving the dynamic performance of star sensors.