The signature extraction and processing are the key aspects of enhancing recognition ability for radar target characteristics. In this paper, to reveal the intrinsic property of the target and improve the accuracy of radar cross section(RCS), we proposed RCS diagnostic imaging technique, extracting the parameters of scattering center model by state space method(SSM), to analyze the signature of GTD-based returns. Comparison with estimating signal parameter via rotational invariance techniques(ESPRIT) method, reconstructing the RCS profile through original and recovery signal, and employing SSM to the PEC sphere simulation, both the signature of specular and creeping wave extraction, the validation of SSM completely achieved the diagnostic imaging by means of parameter extraction.