Atmospheric radiative transfer is investigated to obtain the actual skylight polarization pattern. The simplified double-layer atmospheric model is used to simulate actual atmosphere. The vector radiative transfer equation (VRTE) is solved by means of polarized radiative transfer based on the adding-doubling method (RT3) to get the Stokes parameters of light wave in the discrete points of the sky. Then the skylight polarization information is calculated according to the solution of VRTE. The skylight polarization pattern based on RT3 is built and compared with Rayleigh scattering theory model. The results show that, at the weather conditions of clear sky, cloudy sky and thick cloudy, the degree of polarization (DOP) is gradually reduced, especially for the long wavelength. Simulation results are in good agreement with the traditional Rayleigh scattering theory model. It can also reveal the impact of different weathers, different wavelengths and different albedos on skylight polarization. Therefore it is conducive for the measurement and application of polarized light in actual atmosphere.