In order to study the polarization characteristics of polarized light after multiple scattering through the water body， this paper uses random sampling to fit the phase function of Monte Carlo simulation method to simulate， through model simulation and actual experiments to verify its authenticity. The simulation simulates the polarization state change data of the polarized light with the wavelength of 532 nm through the suspension of polystyrene beads whose particle size satisfies the Gaussian distribution of （600±10） nm. The number of photons in the simulation process is 10⁶. In the experiment， the polarization states of 0° linear polarized light， 45° linear polarized light， left-handed circular polarized light， and right-handed circular polarized light in polystyrene pellet suspension were studied. Both the simulation results and the experimental data show that the degree of polarization decrease of circularly polarized light is at least 20% smaller than that of linearly polarized light. That is， the higher the density of polystyrene pellet suspension particles， the greater the fluctuation in the degree of polarization change，at the same time， the circular polarization is better than the linear polarization in terms of polarization preserving. In the same concentration of water， the polarization state of linearly polarized light with different polarization angles has little difference.