Based on the variation of runoff and sediment flux to the sea before and after the Three Gorges Reservoir (TGR) operation, its influence on change of flow, sediment and riverbed at Yangtze Estuary are summarized. From the aspects of diversion ratios of flow, sediment concentration and scouring and silting at the riverbed, the influence of Yangtze Estuary Deepwater Channel Project (YEDC) on the Yangtze Estuary and the causes of silting of 12.5 m deepwater channel are analyzed.