Under the influence of the polarization effect, the background stray light of the weak starlight simulator and the polarization state of the simulated target star point are doped with each other, so it is difficult to achieve accurate suppression of polarized stray light. In this paper, the mechanism of background stray light induced by the optical engine in a weak starlight simulation device is analyzed, and the principle of mutual doping between stray light and simulated target starlight polarization state is studied. The correlation model of polarization parameters, point source transmittal, and simulated target magnitude was established, and the optimization process of polarization effect was constructed to achieve accurate suppression of polarized stray light in the star map background. The simulation results show that after the optimization of the optical engine, the maximum point source transmittivity is 6.084 × 10 −6 , which meets the 6-magnitude star accurate recognition threshold. The experimental results show that the stray light suppression ability of the weak starlight simulation device is improved by nearly 2 times, and the magnitude simulation accuracy is improved by 1.8 times.