Abstract: An improved four-component decomposition method is proposed based on Polarimetric Interferometric Similarity Parameter (PISP). This method can solve the vegetation component overestimation problems with traditional polarimetric SAR decomposition. The PISP is calculated by three optimized mechanisms obtained from PolInSAR datasets. Therefore, it is sensitive to the dimensional distribution of terrain target, and rotation invariant. The proposed method uses the PISP to improve the volume model. With the improved model, the volume scattering power of different terrain target can be calculated adaptively. The effectiveness of the proposed method is demonstrated with German Aerospace Centers (DLR) E-SAR L-band PolInSAR datasets. The experiment result shows that the building and forest can be well distinguished with the proposed method.