Polarized light is easily absorbed and scattered by raindrops when it is transmitted in a rainfall environment near the ground, resulting in severe attenuation and affecting the target detection ability of the optical system. The transmission characteristics of polarized light under different rainfall conditions were studied to provide a certain basis for polarization detection to overcome the influence of rainfall factors in target detection systems. The Weibull raindrop spectrum was used to characterize the size distribution of raindrops, and the Mie scattering theory was utilized to compute raindrop particle scattering characteristics. The Monte Carlo method was employed to simulate the polarization properties of polarized light after multiple scattering by raindrop particles. Furthermore, the impact of different wavelengths, polarization states, rainfall, and transmission distances on polarization transmission characteristics in rainfall environment was studied. The simulation results show that the polarization degree of the four types of polarized light decreases as rainfall increases, and the transmission distance follows a similar pattern. Under low rainfall conditions, the polarization degree of circularly polarized light exhibits a similar trend to linearly polarized light. However, under high rainfall conditions, circularly polarized light is less susceptible to change compared to linearly polarized light, demonstrating superior polarization retention properties. Furthermore, it is observed that the polarization retention ability of circularly polarized light strengthens with larger wavelengths.