A high-precision real-time star image simulation method is proposed for the emulational test of a marine star tracker. The computation model for star image simulation is established, and the non-stellar elements simulation method is analyzed. The related algorithms are realized by Visual C++ programming. Typical star image simulation examples are presented and compared with the star images generated by Starry Night. The results show that this proposed method can be used to achieve star image simulation for a marine star tracker under various operating conditions. The elements of simulation are complete and correct. The simulation accuracy is comparable to the accuracy of Starry Night at sub-pixel level. And the simulation time for each image is about 24.8 ms. This method meets well the basic requirements of high-precision real-time emulational test of a marine star tracker.