Abstract: The research of radar cross section (RCS) about composite target between ship and sea surface has always been an important and difficult point in the field of electromagnetic computation. In this paper, the sea surface models based on Weierstrass fractal sea surface, the triangular surface element models of target and the electromagnetic scattering models of sea surface target based on physical optics method (PO) and shooting and bouncing rays (SBR) method are set up. A visual electromagnetic scattering estimation system (ESEE) V1.0 is designed by using OpenGL graphic programming technology and C++ multithreading processing technology. Comparing the calculation results of typical target far-field RCS with the commercial software FEKO, the reliability of ESEE is verified. By calculating the RCS of the sea surface under different sea conditions and the composite RCS between the extremely large electric size ship and sea surface, the scattering characteristics of sea surface and the composite targets are analyzed.