Due to the changes in water and sediment conditions of the library after the impoundment operation of the Three Gorges reservoir，which caused riverbed erosion and drawdown in a long distance at downstream of the dam.Chenglingji water level was estimated to drop 1 m to 2 m after the reservoir operation from 20 to 50 years.The effect on Dongting lake area Xiangjiang tail fairway under dry circumstances was evaluated by calculating the water level drops with the hydrodynamic model.The results show that the lake’s waterway surface slope will increase if Chenglingji water level drops 1 m to 2 m under dry circumstances，and water levels and channel depth will reduce significantly in the distance of 80 km from Xiangjiang Dongting lake outlet channel to Xiangjang lake area channel Yingtian beach，which may result in a significant deterioration of waterway conditions.Meanwhile，the renovated shoal’s water depth will not be able to achieve the grade 2 fairway standard.