Abstract: The evolution of water and sediment dynamics is a key indicator of hydrological processes and ecological transformations within river basins. A comprehensive investigation into the mechanisms governing water and sediment transport is essential for elucidating the underlying patterns of their transformation. This study analyzes the characteristics of water and sediment evolution in the Three Gorges Reservoir area using observational data from major hydrological stations from 1955 to 2023. It delineates the influences of the Jialingjiang River, Wujiang River, and the Three Gorges Water Hub Project on this evolution, and establishes a contribution model for quantitative assessment. Results indicate that the Jialingjiang and Wujiang rivers are important contributors to the inflow of water and sediment into the Three Gorges Reservoir, accounting for approximately 29.4% and 30.2% of the total input, respectively. Their respective contributions to changes in water and sediment flux are estimated at 54.1% and 33.0%, while their influence on periodic variations is 30.0% and 46.7%. The regulatory impact of the Three Gorges Water Hub Project on water and sediment processes varies markedly across different stages: the construction phase contributed approximately 58.9% to changes in the water—sediment relationship, whereas the operational phase accounted for approximately 91.1%. However, this influence declined to 78.3% after 2012 due to the effects of upstream cascade reservoirs. These findings offer scientific support for understanding basin-scale water—sediment processes, optimizing regulation strategies for large-scale hydraulic projects, and evaluating their environmental implications.