Abstract: Based on the daily flow series of the confluence area between the Yangtze River and the Dongting Lake during the period from 1990 to 2019, the variation characteristics of the flow in this area were analyzed by using Indicators of Alteration and Range of Variability Approach to evaluate the hydrologic regime alteration degree and ecological effect of the Three Gorges Reservoir in the confluence area.The results showed that: (1)The degree of overall changes in the confluence area was 36.79%, presented the moderate degree of changes. The annual average of 1, 3, 7, 30, 90 day minimum discharge, water rise and fall rate of hydrological indexes changed significantly, showing moderate or high changes; (2)The natural ecological hydrological process in the confluence area was changed by the impoundment of the Three Gorges Reservoir.The change of the hydrological index which is sensitive to the growth and reproduction of four major Chinese carps caused the delay of the spawning period, and the quantity and quality of spawning and reproduction decreased significantly.This study reveals the impact of the impoundment of the Three Gorges Reservoir on the eco hydrological regime of the confluence area, and provides a theoretical basis for the ecological protection of the area.