Abstract: Aiming at the quality control and abnormal diagnosis requirements of on-site withstand voltage test for gas insulated switchgear (GIS), this paper sorts out the standard implementation process of GIS AC withstand voltage test combined with engineering practice, and analyzes the key process control points from four links: pre-test preparation, SF? gas quality control, test wiring and boost control, and conditioning test. The data characteristics and generation mechanism of three typical abnormal phenomena, namely breakdown flashover, partial discharge abnormality and voltage-current mutation, are classified and analyzed, and the abnormal troubleshooting method combining segmented pressurization, partial discharge location and gas decomposition product detection is summarized. Engineering cases show that strictly implementing standardized process control and adopting multi-dimensional detection methods to carry out anomaly analysis can effectively improve the accuracy and safety of GIS withstand voltage test, and provide technical support for the reliable commissioning of equipment.