Based on the historical runoff data of the Changjiang River and the current data from anchor stations within the Changjiang Estuary and its adjacent area since 1950s, some predictive models are established to predict discharges of the Changjiang River at Station Datong from the regulated discharges of the Changjiang River at Station Yichang according to the Three Gorges Project, and on the basis of which impacts of the Three Gorges Project on tida1 currents and residual currents off the Changjiang River mouth are also analyzed. The results show that after the discharge at Station Yichang is regulated, the discharge at Station Datong will be markedly changed and the changed discharge could reach as much as 50 per cent or more in certain months of certain years, which will have a significant influence on the ecosystem. And a secular trend of the discharge reduction at Station Datong will have even greater influence on the ecosystem.