In order to study the electromagnetic radiated interference of electronic transformer caused by VFTO (very fast transient over-voltage) during the operation of disconnector in GIS, the simulation model of 220 kV GIS electronic transformer is established. Taking measured VFTO waveform as excitation source, the VFTO transient electromagnetic field distribution inside metal acquisition box of GIS is calculated. The results show that the transient electric field intensity and magnetic field intensity under VFTO both far exceed the existing electromagnetic compatibility test standards. Suppression methods are also proposed such as reducing the diameter of the terminal block disc and increasing the connection length between metal acquisition box and GIS tank, which can both achieve high shielding effectiveness. These research results can provide theoretical basis and technical support for VFTO electromagnetic radiation interference suppression of electronic transformer.