Ultra-high voltage gas-insulated switchgear (GIS) is a critical core component for ensuring the safe operation of UHV power grids and rapidly isolating system faults. However, operational statistics reveal that discharge faults induced by internal metal particles account for up to 54.5% of GIS failures, with 38.6% of these faults occurring during long-term operation. Therefore, effectively preventing faults caused by metal particle-induced discharge under long-term pressurization has become a primary concern in the operation and maintenance of UHV GIS. To address this issue, this study establishes a full-scale UHV GIS experimental platform to investigate the variation patterns of pulse current partial discharge under long-term pressurization. The experimental results indicate that as pressurization time increases, the frequency, amplitude, and pattern characteristics of pulse current partial discharge signals exhibit specific trends. These findings provide important theoretical insights for fault prevention and optimization of maintenance strategies for UHV GIS. Through this analysis, the study not only reveals the potential risks of metal particle-induced discharge under long-term pressurization but also offers experimental foundations and reference data for further research.