To detect partial discharge (PD) signal from internal defects or particles in gas insulation system (GIS), both couple capacitor (CC) and acoustic emission (AE) methods are applied in the examinations. According to the measured data, we need to distinguish whether it is PD or particle impact signal. From the CC measurement we can determine whether discharge occurs in one of the GIS chambers or not and tell what chambers are possible related to the events. By AE sensors, we can further confirm that whether it is the chamber of PD or particle impact occurred. If there is no discharge events measured from the CC sensors, the AE sensors would be stuck on the chamber to further determine whether particle impact occur in the chambers or not. The signals of particle impact received from the online measurement of GIS are verified through the inspection results of opening.