This paper focus on analyzing the relationship between the polarization signature method (PSM) and the circular polarization method (CPM) for polarization orientation angle shifts estimation induced by terrain slopes variation. The correlation between the two methods is frequently ignored in many studies. For completing this study, we develop a mathematical expression for the PSM by analysing polarization synthesis equation, limiting the polarization synthesize response on linear polarization condition and using a special point to replace the co-polarization signature maximum. This expression will be proved that it is identical with the expression of CPM.