SAR radiometric calibration accuracy is influenced by background clutter. In order to obtain high radiometric calibration accuracy

certain signal and clutter ratio （SCR） requirement must be satisfied or the SCR should be increased by clutter rejection method. This paper studies Active Coded Radiometric Calibration Technique （ACRCT） of SAR and a clutter rejection method based on azimuth signal phase shifter coding and presents the inversion of rang signal frequency modulation. We adopted Range-Doppler imaging algorithm to simulate reference point target and distributed clutter. We also studied SAR radiometric calibration accuracy by peak value method. Experiment results prove that ACRCT could effectively restrain the influence of background clutter signal and improve the precision of radiometric calibration of SAR.