The relations between scattering angle (SA) and the degree of polarization (DOP) of skylights are studied. Measurements under different sky conditions demonstrate that all relation curves between SA and DOP can be described as parabolas. DOP reaches its peak when SA is 90° and the sizes of scattering particles are much smaller than the wavelengths of skylight. The peak value of DOP moves by a small drift when the size of the particle increases. We propose and analyze a polarization dependence model for SA and DOP. Results from simulation are in good agreement with experimental results.