In this paper, the authors deal with partial discharge induced electromagnetic wave investigation on three-phase GIS using UHF method and the application of single-phase Partial Discharge Monitoring device (PDM) on three-phase Gas Insulated Switchgear (GIS). The PD source is a protrusion at different positions on the conductor or on the tank. Frequency and phase spectrums of EMW signals emitted by PD at different positions were observed. The most dominant frequency of EMW signal in three-phase GIS was estimated from the cut-off frequency (fc) formula for single-phase GIS.