Abstract: Fast and accurate solution of a corner reflector's radar cross section is the important foundation of synthetic aperture radar radiometric calibration. Since a corner reflector used in radiometric calibration is usually electrically large, its backscatter field is appropriately analyzed with a high frequency approximation method;a fast and accurate solution is proposed in this paper. The incident field and its corresponding illuminated area are determined by a ray tracing of a incident wave and reflected wave, then the backscatter field of each illuminated area is computed by the Gordan surface integral method respectively and added up for the total RCS of a corner reflector. Simulation results agreed well with the results from the references and from the electromagnetic computing software FEKO. So the method proposed in this paper was demonstrated to be accurate and efficient, and especially suitable for fast radar cross section computation of corner reflectors composed of large size plates.