Abstract: Ouchi Estuary serves as a critical flood channel linking the Jingjiang River and Dongting Lake,and its flow-sediment diversion variations directly govern regional flood control,water resources and ecological security.Measured data are applied to analyze evolution features and driving mechanisms of Ouchi Estuary’s flow-sediment diversion after the Three Gorges Project impoundment,and a 2-D horizontal flow-sediment mathematical model predicts its future trends.Results show that Ouchi Estuary’s flow diversion ratio and sediment diversion ratio drop by 32.9% and 48.6% respectively during 2003~2024 compared with 1990~2002,with continuous diversion capacity degradation.Uneven riverbed erosion inside and outside the estuary and persistent siltation-upstream extension of Tianxingzhou mid-bar nearby degrade inflow conditions under medium-low water stages.Model predictions indicate dominant channel erosion over the next 20 years.Uneven erosion further accelerates diversion shrinkage and worsens flow cutoff events.The cutoff discharge threshold rises from the present 9 760~12 700m³/s to 15 000~17 300m³/s.Two regulation alternatives,dredging-widening of the existing diversion channel and dredging-widening of a new diversion channel,are proposed to mitigate diversion shrinkage.Model validation proves both schemes improve low-water diversion capacity and reduce flow cutoff days.The existing-channel scheme delivers more stable medium-long-term performance.These findings provide scientific basis and technical support for river-lake comprehensive management and water-system-connectivity ecological restoration in the middle Yangtze River.