Significant degradation have occurred in the middle Yangtze River since the operation of the Three Gorges Project. In the current study, longitudinal evolution differences of different reaches along the middle Yangtze River were quantitatively compared, and the main reasons were investigated. In terms of planform geometry, the intensity of bank retreat and central-bar deformation showed a decreasing trend along the reach, and it was most significant in the Jingjiang Reach. With respect to cross-sectional geometry, channel degradation developed gradually from the Yizhi Reach to downstream reaches. It is uncommon that the adjustments of bankfull channel geometry in the upper Yizhi Reach were smaller than those in the downstream reaches. The reason is that the significant coarsening of bed-material composition in the upper Yizhi Reach hindered the development of channel degradation. In terms of discharge capacity, the variations of reach-scale bankfull discharge in the Yizhi Reach were mainly controlled by the incoming flow and sediment conditions, and it increased with the process of channel degradation. In the other subreaches, the variations of bankfull discharge were mainly influenced by the backwater effects owing to the confluences of tributaries and lakes.