Abstract: In the present work, spatial and temporal changes of hydrological regime in the middle reaches of the Yangtze River after the impoundment of the Three Gorges Project were quantitatively evaluated, which provides a scientific evidence for the ecological protection of the middle reaches of the Yangtze River and regional water resources management. The range of variability approach was used to analyze average daily data for discharge and sediment concentration from five hydrological stations on the stem stream of the Yangtze River. Thus, river sections with the maximum water and sediment variation degree in the middle reach of Yangtze River and hydrological index categories and their corresponding ecological effects after the impounding of Three Gorges Project were quantitatively evaluated. The results showed that the changes of sediment concentration downstream were far greater than that of discharge after the impounding of the Three Gorges Project, which had a large scale decline compared with that of before the impounding except for Chenglingji station. Decrease range of sediment concentrations in Yichang station attained to one order of magnitude. The regulations of Dongting Lake on sediment concentration were obvious. Variation of discharge decreased with the increase of the distance from the dam, with a decrease of flow obvious between July and November. These changes in hydrological regime will affect both the fish-spawning habitat downstream and the growth of the aquatic organisms in the retarding area and the surrounding vegetation.