The invention discloses a site calibration method for a GIS current transformer. The site calibration method includes the steps of sending out a frequency conversion signal with a preset frequency, amplifying the frequency conversion signal, outputting the frequency conversion signal to the GIS current transformer, returning a feedback signal through the GIS current transformer to conduct amplitude limiting on the feedback signal, conducting frequency-selecting filtering, tracking multiple signals, feeding back tracking detection signals, conducting calculating, analyzing and processing on the feedback signal and the tracking detection signals, outputting a frequency transformation signal and a switching control signal, changing the frequency of the frequency conversion signal according to the frequency transformation signal, switching the sampled signals according to the switching control signal, repeating the steps, and obtaining the calibration result through multiple times of measurement according to the comprehensive sampling and processing result. By means of the site calibration method, interference of most power frequency signals on the site can be avoided, and rapid and accurate error detection can be carried out.