The Monte Carlo simulation method based on phase function fitting with random sampling is used to simulate the polarization characteristics of polarized light after multiple scattering by ellipsoidal particles, and its correctness is also verified by experiments. The ellipsoidal yeast particles with a long and short axis ratio of 1.5 are taken as study target, and the polarization transmission characteristics of laser are studied when propagating in soot. The polarization changes of 532 nm laser with 0° linear polarization, 45° linear polarization and left circular polarization are investigated during the ellipsoidal particle diffusion process. The results show that the higher the ellipsoidal particle concentration is, the greater the randomness of the polarization degree change is. Moreover, the polarization-maintaining property of a circularly polarized light is better than that of a linearly polarized light. At the same concentration, the effects of linearly polarized light with different polarization angles on polarization state are not much different.