A study for discharge pattern analysis partial and fault location by use of UHF sensors in GIS. However, in the latter case, the results considered the velocity of EM waves modified by the waveguide characteristics of GIS bus bar were not reported yet. In this paper, UHF wide band sensor to detect partial discharge signals have been designed and manufactured to get the widest band characteristic by an application of Fat-Dipole UHF antenna and the result that the transmission velocity of EM waves is 2/3 of the light have been got through the consideration of waveguide characteristics. Also, to verify applicability on site of the developed method, self-designed external type UHF sensor have been installed on operating GIS in Korea Midland Power co. and detected location of the fault. Through the fault have been found at the location, the reliability of the developed method have been proved.