Abstract: Bcause of the sharp spatial difference in water resource distribution, the present serious water shortage problem and the future increasing demands for water resource in the North China, the large-scale south-to-north water diversion will become an inevitable trend.this paper studies the effect of such engineering works on the coarse-grained sediment output into the Yangtze River Estuary under the background that about 10% of the total Yangtze River runoff discharge were diverted to the other drainage basins in the North China.The study indicates that under the typical hydrological years, for examples, 1978, 1978, 1983 representing dry year, ordinary year and flood year, respectively,a reduction of about 3 000m³/s runoff discharge to the sea from the typical discharge level 23 000m³/s, 30000m³/s and 40 000m³/s would result in a decrease of sediment discharge(>0.05mm in grain-size) ranging from-39% to-24% of the total sedunent output, corresponding to 2350×10⁴-4700×10⁴ tons in the sediment amount.The relationship between the monthly mean runoff discharge and coarse-grained sediment discharge shows that under the higher runoff discharge, the percent of decrease is smaller, but the absolute decrease in sediment amount become greater.Such a reduction of coarse-grained sediment discharge into the estuary is expected to exert significant effect on the estuarine and coastal sediment dynamics and morphodynamics in the coming 21st century.