The diverted flow from three outlets of Jingjiang River is an important part of inlet flow of the Dongting Lake. Its changes would affect the relationship between the Yangtze River and the Dongting Lake. Since the impoundment of the Three Gorges Reservoir, changes in the diverted flow from the three outlets has been closely related to incoming flow decrease and runoff process change in the Yangtze River. In this article, according to measured data, the relationship between discharge of mainstream Jingjiang River and diverted flow of three outlets was analyzed, and the durations of middle flow and high flow of mainstream Jingjiang River before and after the reservoir impoundment were compared. Moreover, the influence of runoff process change caused by reservoir storage on the three outlets was also researched. Results revealed that 1) the diverted flow from three outlets is dependent on the number of days of middle flow and high flow in mainstream Jingjiang River. The diverted flow from three outlets reduced due to decreases in incoming flow and middle-and-high-flow durations caused by reservoir storage and regulation; 2) in running period of 139 m water level, the reservoir runoff changed slightly, which had no big influence on the three outlets; 3) in typical year of running period of 156 m water level, impoundment process has the biggest influence on three outlets, with the total diverted flow decreasing by 770 million m³, whereas in other periods the influence was small; 4) in running period of 175 m water level, flood storage in flood season and impoundment in storage period significantly affected the duration of middle flow and high flow in Jingjiang River, causing a decrease of 8.31 billion m³ in total diverted flow of three outlets.