Abstract: In recent years, due to local river regime adjustments and the prolonged service life of certain revetment works, the frequency of bank collapse along protected slopes in the mainstream of the middle Changjiang River has shown an increasing trend. Further clarification of the influencing factors and their mechanisms of action on protected bank slops is of great significance for river regulation in the middle reaches of Changjiang River. This study selected the bank collapse events that occurred in April 2025 in the Tuanjie Sluice Reach of Jianli in the middle Changjiang River, as a typical case. By using measured data analysis methods, the causes of bank collapse were examined from the perspectives of geological conditions, hydrological conditions, riverbed deformation, and human activities. Emergency protection recommendations and medium-to-long-term regulation strategies for Tuanjie Sluice reach were preliminarily proposed. The results indicated that: the geological structure of Tuanjie Sluice Reach was a typical "upper clay and lower sand" formation. The main flow had long been flowing along the bank, causing severe toe scouring during the dry season. Three new scour holes were formed near the 2025 collapse site, with the maximum scour depth reaching 6 m at the nearest one. A relatively pronounced sudden drop in water level occurred at the upstream Jianli Station during the collapse period, and the navigable boundary for vessels in this reach was at an average distance of 26. 48 m from the dry-season water level platform of the bank slope, indicating that the navigation channel was relatively close to the bank. The findings demonstrated that adverse geological conditions and sustained near-bank flow scouring were the primary causes of the collapse of the protected slope at Tuanjie Sluice, while sudden water level drawdown and ship-induced waves are secondary factors.