Graphical electromagnetic computing (GRECO) is an effective method of predicating the radar cross section(RCS) of complex targets, but there must beforehand be a model file from which the shape parameter can be easily obtained. Based on the GRECO, the model file generated by several commercial shaping software could be converted to the type fitting for the RCS calculation by means of the commercial software RHINO. The processing method of data had a wide use and may not delimit any details of model. The multi-screen display calculation methodwas used to improve the precision of calculation when predicting the RCS of electrically large and full size targets. By using display list technology of OpenGL, the program expended less time than before. A simple approach was also presented by which the scattering source of targets can be analyzed expediently. The good agreement between the calculating results of our method and that of plate-edge method indicates that this method possesses practical value in engineering.