Abstract: In field radar cross section (RCS) measurements, the on-site relative calibration method is typically used for calibration. However, this method requires repeatedly setting up the target, which is a cumbersome operation, and frequent target replacement can easily lead to changes in the test background, introducing measurement errors. To address this issue, the off-site calibration method used in far-field RCS testing has been introduced to outdoor close-range testing in this paper. First, ground-bounce illumination gain and the electromagnetic wave attenuation due to distance at different target positions are analyzed. Then, the factors influencing the ground-bounce illumination gain are verified by means of experimental testing. Finally, a rapid and accurate measurement of target′s RCS is achieved by utilizing on-site collected data and applying a series of methods, including background vector cancellation, Fourier transform, frequency-domain windowing, ground-bounce illumination gain compensation, and distance compensation. Experimental results show that the mean error of measured RCS falls within 0.5 dB, and the root mean square errrors of both the RCS curve in frequence domain and the theoretical vlaues fail to exceed 1 dB. The method proposed in the paper validates the feasibility of off-site calibration method in outdoor close-range RCS testing.