It is very important that a GIS on-line detecting system is built availably, and it is also the key to acquiring successful detection. And it is of great significance to find out which parts are liable to faults as well as their real discharge characteristics. By using an ultra-wideband partial discharge detecting system, the discharge signal from disk-type spacer in key part of 1lokV GIS is acquired and studied. These key parts are the part nearby PT, the part nearby CT, the part nearby CB, the part nearby bus, the part nearby the LA. According to the different machine structure and electromagnetic field non-uniform distribution, these disk-spacers have different partial discharge characteristics. It is found that spacers in different parts of GIS have their own partial discharge characteristics, and their discharge frequencies concentrate below 300MHz, which provide numerical reference for the on-line monitoring of GIs.