Different state of polarization can be generated by different soil moisture, which relates closely to the wavelength, the roughness of the soil, the component of soil, and the incident zenith angle. According to Kodis[EQUATION] theory for scattering by a rough surface, a simple formula that relates the degree of polarization of soil to incident zenith angle, viewing angle and refractive index is obtained. Polarized reflectance data of different moisture red soil is collected with a polarimetric instrument and compared with the calculated results. Preliminary results of the change in degree of polarization for red soil with different moisture are presented. The results are significant for satellite agricultural remote sensing.