In China, above of 110kv voltage class of the grid mainly adopts SF6 gas insulated switchgear ,especially the application of GIS equipment in the power grid is more and more widely. With the increase of voltage level and system capacity,SF6 switchgear equipment internal insulation faults in the power grid probability tend to rise, thus equipment defect and state judgment is one of the key problems to be solved. Aiming at this problem, this paper mainly studies the typical defects development mechanism in SF6 gas insulated switchgear and signal characteristics of different stages of development, focusing on detection methods of SF6 switchgear partial discharge based on the Ultra high frequency and Acoustic emission detection, and conduct some tests and researches about the typical defects discharge of GIS and the development process. In the last, the Characteristic spectrum Development Law and Diagnostic methods were proposed, a typical cases of GIS partial discharge are analyzed.