The Jingjiang Three Outlets (JTO) are important channels connecting the Yangtze River and Dongting Lake. Changes in these channels after the Three Gorges Dam operation have affected water flow. By studying channel changes from 1980 to 2014, it was found that the water level with the same discharge decreased in the upper Jingjiang River due to channel incision. In contrast, the water level with the same discharge increased at the JTO due to channel deposition. These channel changes caused a significant decrease in discharge diversion at the JTO, with channels contributing to about 37.74% of the decrease in amount and 76.36% in ratio after the dam's operation. Channel changes are the main reason for the decrease in discharge diversion ratio, but not the main reason for the decrease in the amount of diversion.