The impact of water cloud optical properties on atmospheric polarization properties is researched, and atmospheric polarization pattern under water cloud condition is simulated. By using the polarized radiative transfer based on Monte Carlo model, the changes of atmospheric polarization properties with the optical thickness and effective radius of water cloud from 350 nm to 700 nm are simulated. By calculating Stocks vector of discrete points in the whole sky, atmospheric polarization pattern of water cloud is researched and compared with the polarization pattern of clear sky. The results show that the degree of polarization (DOP) decreases with the increasing of water cloud optical thickness, which is more obvious with the wavelength upward trend. DOP decreases with the fall of effective radius to a certain extent, but it has less influence on short wavelength. With the increasing of solar altitude angle, DOP of the whole sky becomes lower. The area of DOP at about 0 makes the angle of polarization (AOP) imprecise. The research on atmospheric polarization pattern of water cloud provides theoretical basis for the specific application of polarization navigation sensor.