Field experiment and CFD numerical simulation were performed to improve the ventilation and operation modes of Yixing pumped storage power station. Main influencing factors on air distribution including the air supply velocity, the start and stop combinations of generator units, and the modes of generator exhaust air cooling were investigated. The change rules of the energy utilization coefficient η, the temperature inhomogeneity coefficient k_T, the velocity inhomogeneitycoefficient k_u in a typical underground powerhouse floor were analyzed. The results show that under the existing design scheme, the temperature near the heat source equipment is significantly higher than the average temperature in the plant but the relative humidity near the heat source equipment is significantly lower than the average value in the plant. The air flow velocity near heat source equipment increases due to natural convection. The temperature, humidity and velocity distribution in the generator floor basically meet the design requirements, but in typical hot wet seasons, the temperature and humidity are close to the upper limit.