Abstract: To address the problem of changes in river water and sediment fluxes into the ocean, the Yangtze River was used as a subject of this study based on the field measurements of water, sediment and rainfall data at Datong station and its components from 1950 to 2017. By analyzing the processes of changes of the water and sediment entering the ocean and the various components and their contributing ratios, the principal contributing components were determined, and the trends of changes in water and sediment fluxes into the ocean were predicted. The results show that: (1) The annual runoff of each component and the rainfall had not changed much for many years, and as a consequence, the change in annual runoff from Datong station into the ocean had been unobvious. The contribution of Yichang station to the annual runoff to the ocean was 48%. (2) The intra-annual process of water flux from Datong station into the ocean gradually became more evenly distributed, with Yichang station as the primary contributing component, and the average contributing ratios during the flooding and low water seasons were 233.79% and 80.36%, respectively. The primary contribution of Yichang station reflects the smoothing effect of the upstream cascade reservoir group on the process of water flux from Datong station to the ocean. (3) Basin reservoir construction tends to maintain the flattening effect on the intra-annual process of water flux from Datong station into the ocean and the stabilization of the annual runoff. (4) The annual sediment load at Datong station had decreased significantly since 1985. The sediment at Datong station was primarily from Yichang station before the impoundment of the Three Gorges Reservoir, and the contributing ratio was 116.04%. After the impoundment of the Three Gorges Reservoir, the sediment at Datong station was mainly replenished from the riverbed along the reach between Yichang and Datong, and the contributing ratio was 53.29%. The gradual reduction in riverbed replenishment downstream of the reservoir and the prolonged reservoir sedimentation time are expected to prevent the average sediment load entering the ocean from exceeding 1.5 × 108 t/a for a long period of time (> 300 years).