In terahertz regime,the parabolic reflector antenna(PRA)targets are electrically very large targets.The CAD model of the PRA was simulated with the electromagnetic scattering computation software CST Microwave Studio.The radar cross section(RCS)of PRA was solved by the high frequency asymptotic solver in X waveband and terahertz regime.The RCS characteristics,high range resolution profiles and inverse synthetic aperture image of the target are researched and analyzed.