At different wave band and polarization, the high frequency RCS of a model was computed with the graphical electromagnetic computing (GRECO) method. The shadowed and eclipsed surfaces were identified by using the visualization hardware, and the unit normal to surfaces were got with 5 light sources through 2 times of illumination. While computing the mirror-scattering RCS, 2 Sinc-functions were used to avoid singular points in physical optics (PO) results and method of equivalent currents (MEC) was used to compute the reflection of the edges. The agreement of the final computation results with the experimental data indicates this method could be used to estimate the model's RCS quickly and effectively at engineering analyses. Having added the interface that can identify and read IGES files, the limit to the type of the modeling files is released and the GRECO method's application range is extended.