The presence of latent metallic foreign matter in gas insulated switchgear (GIS) poses a potential threat to insulation reliability. Conventional withstand voltage tests are difficult to effectively detect such foreign matter. In this study, an externally applied vibration withstand voltage test method was proposed and implemented. Mechanical vibration excitation was introduced into a 550 kV GIS, combined with ultra- high frequency (UHF) and ultrasonic signal analysis, to explore the particle motion characteristics and discharge behavior. Experiments have shown that external vibration can significantly activate metal particles that are dormant under static voltage, causing them to move and induce partial discharge. Through multi-voltage level pressurization and synchronous excitation, combined with high-speed cameras, ultrasonic sensors and UHF detection systems, dynamic monitoring of particle movement phenomena and discharge signals is achieved. The results show that after excitation, the discharge amplitude of the UHF signal and the ultrasonic triggering frequency have obvious changes, and have good followability; after excitation, the particles will have obvious movement, and the ultrasonic signal can detect this movement well; no obvious frequency change was found in the UHF signal before flashover, and the flashover signal is difficult to detect on-site. This study provides a new test method and analysis basis for GIS insulation reliability assessment and latent foreign matter detection.