Abstract: Since the storage capacity coefficient of pumped storage power stations is high, so the initial water impounding process is relatively complex, then a reasonable and accurate analysis on the initial water impoundment is of great significance for optimizing construction progress, engineering design schemes, and achieving project benefits.In this paper, an analysis model for initial water impoundment calculation was constructed based on the characteristics of water balance during the initial storage process of pumped storage power stations.Three methods, the long-series method, the typical impounding period method, and the monthly impounding period method, were used to calculate the water inflow process of the upper and lower reservoirs at 75% frequency.Taking the Shitai pumped storage power station as an example, the surplus and deficit of available storage capacity for each impoundment period group under different methods were compared and analyzed.The results showed that the runoff process significantly impacted the surplus water volume analysis in each impoundment period group of the pumped storage power station.The initial water storage deficits of the Shitai pumped storage power station, calculated by the long-series method, the typical impounding period method, and the monthly impounding period method, were 3.18 million m³, 2.28 million m³, and 2.85 million m³, respectively.Among these, the monthly impounding period method aligns most closely with the long-series method in terms of the water supply process and the assessment of water storage surplus or deficit for each impoundment period group.The research findings can provide a reference for the initial water impoundment analysis and the design of water replenishment projects for pumped storage power stations.