Abstract: This study addresses the challenges of high energy consumption and difficulty in regulating the thermal environment within ventilation systems of large hydropower station underground cavern groups. Taking a 640 MW hydropower plant as the research object, a one-year continuous field monitoring campaign was conducted to systematically analyze the spatial and temporal distribution characteristics of the temperature field in key caverns, including the main powerhouse and cable tunnels. The research identified equipment heat dissipation, ventilation operation mode, external environment, and geological conditions as the key influencing factors, among which the ventilation operation mode proved to be the most effective control measure. Based on these findings, comprehensive optimization strategies were proposed, including stratified air supply, localized enhanced ventilation, and demand-based dynamic air volume regulation. Engineering application demonstrated that after optimization, the average temperature in the main powerhouse decreased by 4.2%, and the overall energy consumption of the ventilation system was reduced by 15.1%, achieving the dual objectives of thermal environment improvement and energy saving. This study establishes a data-driven approach for optimizing ventilation in underground cavern groups, providing a theoretical basis and engineering reference for the design and efficient operation of similar projects.