Abstract: Antenna of low frequency SAR usually has very wide azimuth beam width along track. The changes of the RCS of the calibrator with the incident angle of electromagnetic wave cannot be neglected during the radiometric calibration. In this paper, RCS of the calibrator as a function of incident angle has been calculated at low frequency using MOM. Combining with the theory of strip-mode SAR, a calibration method is proposed and computer simulation is used to verify the validity of this calibration method. Simulation results verified the effectiveness of this method.