How to radiate ultra-high-frequency（UHF）verification signal into GIS without internal UHF antenna is one of the key problems in field sensitivity verification for partial discharge detection instrument. To solve this problem

metal flange style UHF verification signal radiation method is suggested

in which UHF signal is radiated into GIS through the hole in the metal flange outside the insulator. Attenuation of the UHF signal passing through the small hole is explained with the theory of engineering electromagnetic compatibility. UHF signal test instruments are built up based on a 252 kV GIS. The consistency of verification signal and partial discharge signal is analyzed by comparing their power spectrums and attenuations. Conclusions are drawn that: 1)the attenuations become smaller with frequency rising; 2)the power spectrum and attenuation of the verification signal are similar with that of the partial discharge signal

and the energy of the verification signal is smaller than that of the partial discharge signal when the frequency is below 600 MHz. The output amplitude and rise time of the pulse should be increased so that the amplitude and spectrum of the injected signal and the paritial discharge could be similar in the on-site verification. This work may be applicable to field sensitivity verification of UHF PD detection instrument installed on GIS.