The operation of the Three Gorges Reservoir (TGR) has altered water and sediment processes in the middle and lower reaches of the Yangtze River, affecting the adjustment characteristics of scouring and sedimentation in the branch channels as well as the flow distribution relationships among relatively balanced channels. Thereby exerting a cascading impact on flood control, navigation, and river management. Given the current limitations in understanding the adjustment patterns of branch channels under the influence of water and sediment conditions altered by the operation of cascade reservoi, this study utilizes measured hydrological and topographic data from 2003 to 2023. Taking eleven typical distributary channels in the Chenglingji to Jiujiang section as examples, it employs a distributary channel classification method based on dynamic diversion ratios to investigate channel type conversion phenomena and analyze their driving mechanisms. The study reveals：（1）The method for classifying branch channels based on dynamic diversion ratios demonstrates good adaptability in classifying branch channels in the middle and lower reaches of the Yangtze River and identifying their typological transitions under different operating modes of the TGR（2）Following the TGR impoundment, the branch channels exhibited different adjustment patterns during various periods. Since 2013, the section from Chenglingji to Jiujiang has been dominated by Type I branch channels (where the main channel corresponds to a low-flow-dominant branch channel), while in Type II branch channels (where the main channel corresponds to a low-flow-prone branch), the Jiepaoxin Sandbar branch section, Luxi Kou, Jiayu, and Yanzowo channels have transitioned to Type I branch channels, shifting from a “main channel shortening, branch channel lengthening” pattern to a “main channel lengthening, branch channel shortening” pattern;（3）For the transformation of Type II distributary channels into Type I channels, altered hydrological and sediment conditions were the primary driver. Navigation improvement projects demonstrated a promoting effect on this transformation in most distributary channels. After 2013, the frequency and duration of flow levels between 20,000 and 30,000 m3/s increased, leading to intensified scouring in the main channel branch at these flow levels. with some branches evolving into Class I distributary channels. It is foreseeable that branched river systems in the middle and lower reaches of the Yangtze River will predominantly shift toward Class I, characterized by an adjustment pattern where the main channel grows while tributaries diminish.