This paper presents a new method for computation of the monostatic radar cross section (RCS)of electrically large conducting objects. Compared with the traditional Z-buffer technique, the improved onecan record not only the illuminated surface or the body, but also the information about the shadowed part.So, multi-scattering and RCS or cavity can be calculated. The second advantage or it is using dual representation of the target’s racet surface, in which the illuminated part is treated as bicubic patches for RCS calculation, and is simplified to flat facet when ray tracing is done. Excellent agreement with the experiment hasbeen obtained. Compared with the traditional Z-buffer technique, the improved one can record not only the illuminated surface or the body, but also the information about the shadowed part.So, multi-scattering and RCS or cavity can be calculated. The second advantage or it is using dual representation of the target’s racet surface, in which the illumination part is treated as bicubic patches for RCS calculation, and is simplified to flat facet when ray tracing is done. Excellent agreement with the experiment hasbeen obtained.