To clarify the homogenization trend of river discharge induced by water conservancy projects represented by the Three Gorges Reservoir, this study analyzes the long-term intra-annual and inter-annual variations in river discharge in the middle and lower reaches of the Yangtze River based on observed data and using trend detection methods. The results show that a homogenization trend in river discharge has been present since the 1950s; however, the operation of the Three Gorges Reservoir in 2003 intensified this trend from statistically insignificant to statistically significant levels. During the reservoir impoundment period, discharge decreased, while discharge during the dry season increased significantly. Notably, the homogenization trend is more pronounced in the middle reaches than in the lower reaches. At Yichang station, the coefficient of variation experienced an abrupt reduction in 2003, and the homogenization trend increased significantly, while at Datong station the same shift occurred in 2013. The homogenization of river discharge also has implications for tidal wave propagation and the nonlinear interaction of tidal constituents in the estuary.