Abstract: This paper briefly described the entire process of detection, analysis, and operation and maintenance decision-making for internal discharge defects in 750 kV GIS equipment.It focused on the ultra-high frequency, ultrasonic, and X-ray detection methods used for identifying discharge defects, as well as the comprehensive analysis and diagnostic approach. By synthesizing data from the three detection methods, the discharge location, cause, and severity were accurately determined.This provides a technical basis for subsequent maintenance and inspection of the equipment, ensuring its safe operation and effectively maintaining the reliability of power grid supply. The research can serve as a reference for condition monitoring and defect diagnosis of 750 kV GIS equipment.