For nematic liquid crystal samples with a thickness of tens of microns or doped with rod-like dye molecules, anisotropic scattering and absorption will have a significant or even dramatic impact on polarization detection. The ideal polarization analysis model without considering absorption and scattering loss will no longer be applicable. In this paper, a more universal polarization detection system for measuring reorientational angle of nematic director is designed. A polarization analysis theory considering anisotropic absorption and scattering is given. A reliable and stable test scheme and a specific data processing method are given in combination with the practical testing.