Abstract: In recent years, the research of compact polarimetric (CP) modes has caught attention . By using the full polarimetric (FP) mode, the existence of orientation angle (OA) induced by terrain slope will lead to the difficulty in post-processing, such as terrain targets classification and identification. In the paper, the OA estimation is derived and analyzed by using the scattering vectors of CP SAR modes. Recurring to the circular polarimetry, the OA can be evaluated from the CP SAR data. And the experimental results based on measured data sets have been shown to improve the estimation methods, while analyzing the practicability of the estimation under CP modes and its value in engineering application.