Abstract: Taking lightning hit withstand test of GIS for the underground power station of Three Gorges hydro-junction as a case, the principle, equipment and procedures of test are described in detail. The electric discharge phenomena occurred in the test process, and the problems existed in waveform selection for the test devices of large electric capacity during the test and installation of GIS. The causes for the discharge and other problems were analyzed. The results could provide reference and guide GIS lightning hit test for power stations.