Abstract: The fast computing method of radar cross section (RCS) for military aircraft stealth designing is an important research subject. The proposed method employs physical optics calculation (PO) to compute the scattering contribution of the surface unit cells and uses the improved method of equivalent currents (IMEC) algorithm to compute the wedge scattering contribution of target edge consisted of the crossing surface. The scattering field of total target includes above two parts of contribution. Having the models of calculation, RCS of aircraft can be simulated. The simulation results are compared with the testing ones and show the satisfied outcome. The proposed method of calculating RCS can be used in engineering application.