Based on the sediment supply from the Yangtze River and the analysis of the accretion and erosion of the subaqueous delta at the Yangtze River Estuary in ten years before and after the impoundment of Three Gorges Reservoir in June of 2003, we discussed the effect of Three Gorges Reservoir on the evolution of landform of the Yangtze Estuary delta. The results showed that, (1) From the impoundment of Three Gorges Reservoir (2003-2008), about 73 per cent of sediment from the upper reaches had been intercepted into the reservoir, nevertheless, influenced by river bed erosion of the lower reaches and by sediment supply from tributaries of the lower reaches, the impoundment of Three Gorges Reservoir had caused 49 per cent decline in the bedload sediment transport rate of Datong Station; (2) the net silt accumulation of the study area (1500 km2) was 7.25 x 108 m3 (1.21 x 108 m3/a), -1.03 x 108 m3 (-0.26 ×108 m3/a) and-0.20x 108 m3 (-0.05x108 m3/a) respectively in 1994-2000yr, 2000-2004yr and 2004-2008yr; (3) Most of the area over 7 m depth has been in erosion backward in the study area since 2000, especially the area of 10-20m depth. At the same time, the tidal-flat area (within 5 m isobath) accumulated more intensely than that did in the preceding period of time. The conclusions were that the impoundment of Three Gorges Reservoir accelerated the decrease of the sediment form the Yangtze River which was the main cause for the change from accretion to erosion of the subaqueous delta, and half of the new erosion in the study area was induced by Three Gorges Reservoir in recent years. The tidal-flat area had been accumulating but corrading in recent years due to a series of estuary major projects.%根据长江三峡蓄水前后十余年的入海泥沙通量和河口口门区冲淤的对比分析,初步探讨三峡工程对长江河口三角洲地貌演化的影响.结果表明:(1)三峡水库蓄水以来(2003-2008年),入库悬沙73％以上被拦截在水库里,因坝下游河床冲刷和支流来沙补给,三峡水库蓄水导致大通站输沙率下降49％； (2) 1994-2000年、2000-2004年、2004-2008年,长江口门研究区(1 500 km2)净淤积量分别为7.25× 108 m3(1.21亿m3/a)、-1.03×108 m3(-0.26亿m3/a)和-0.20×108m3(-0.05亿m3/a); (3) 2000年以来,河口门外水深超过7 m的大部分区域处于蚀退,尤以10-20 m区域侵蚀最为强烈,但河口滩地(5 m线以内)较前一时段淤积加强.主要结论:三峡水库蓄水加剧了长江入海泥沙的减少；入海泥沙减少是长江三角洲从淤积转为侵蚀的主要原因,近几年入海泥沙减少和河口口门区出现的冲刷有一半左右可归因于三峡工程的运行；河口滩地的逆势淤积是近年一系列的河口重大工程影响的结果.
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