Silting-up is an important factor to have an impact on lake function.The increase or decrease of the discharge, after Three-Gorge Project goes uito operation, will change the sand exchange and silt deposition in Poyang Lake.According to the sedimentary characters of Poyang Lake9 this paper predicts the change in erosion and deposition with discharge by using the typical hydrological years, and the result shows that the biggest increasing range of silting up intensity is about 7.2% in March-April,the decreasing range less than 1% in October and no change in other months.Assessment of erosion and deposition in the whole lake indicates that the sedimentary rate decreases a bit in the lake area to the south of Xinzi and increased by 0.13 mm/a to the north.However, the range of erosion and deposition change is not the same as it in different years, which is related to the original lake level and the regulated level change near the outlet of lake.Its deposition rates, therefore, will tend to be low.It proves that there will be less change in lake sedunention and erosion rate after Three-Gorge Reservoir goes into operation.However, the negative effects of river beach development and the lake outlet section narrowing should be paid vigilant attention to.