The invention discloses a field calibration system for a GIS current transformer. The field calibration system is externally connected with the GIS current transformer. The field calibration system comprises a frequency conversion signal generator, a power amplification unit, an output protection unit, an input protection unit, an amplitude limiting protection unit, a frequency-selecting filtering unit, a multi-path signal tracking unit, a signal conditioning unit, a signal switching sampling unit, an ARM and DSP processing unit, a first protection unit, a second protection unit, a third protection unit and a wide-voltage switch power source. The field calibration system for the GIS current transformer can avoid the interference of most field frequency signals, an error test can be rapidly and accurately conducted, and the safety of a system, a device and a person can be protected.