Climate change and human activities have led to changes in the water resources of the Yangtze River Basin in both annual and monthly scales. By using different trend analysis and abrupt change analysis methods, the water inflow trend at the Three Gorges dam site was examined based on inflow data from 1890 to 2020. The changes of water inflow in annual average scale, in water level drawdown period, in flood season, and in impoundment period at the Three Gorges dam site before and after the construction of the Xiluodu, Xiangjiaba, and Three Gorges Reservoir projects were also scrutinized. Results revealed that the inflow at the Three Gorges dam site showed a significant decreasing trend in annual average, in flood season, and in impoundment period, but an insignificant decreasing trend in the water level drawdown period. The inflow trend changed abruptly around 1960. The Xiluodu-Xiangjiaba Reservoir’s water supply downstream during dry season led to an increase in the inflow of the Three Gorges dam site, implying that giant reservoirs have a great impact on the temporal and spatial distribution of water resources in the upper reaches of the Yangtze River and the Jinsha River.