The calibration reference point targets’ Radar Cross Section (RCS) is a inherent property depending on frequency and incidence angle, for traditional SAR systems, which can be approximately regarded as a constant under the condition of narrowband and narrow beam. However, for high-resolution SAR systems, replacing the RCS in the case of wideband and wide beam by the RCS of central frequency and azimuth aspect, will result in an inaccurate radiometric calibration output. In this paper, correction methods of reference point targets in the echo domain or in the complex image domain are presented. From the experimental result of simulation and ground-based SAR, it can be seen that the absolute calibration factor varies over 1.2 dB before and after the reference point target correction. The results of real data show that point targets in the SAR image are more symmetric after correction of reference targets’ radiometric characteristic, and the main lobe in azimuth becomes narrower, which is more close to ideal point target impulse response in time domain, thus validating the effectiveness of the correction algorithm.