Abstract: Most studies on the sediment delivery of the Three Gores Reservoir (TGR) focus on the reduction of siltation in the reservoir area, while the impacts on the river bed evolution in the downstream reaches need further study.This study is of great significance for optimizing flow and sediment regulation as well as the protection and utilization of downstream reaches.The river bed evolution impacted by sediment delivery regulation during flood season in the Jingjiang reach was studied, which located downstream of the TGR.Combined with the measured data, a 2-D flow-sediment numerical model in the Jingjiang reach was established to calculate and analyze the erosion and deposition process by setting different sediment delivery ratios (7%—100%), based on the sediment delivery regulation in July 2018.The results showed that, although the Jingjiang reach was generally suffering an annual scouring process, it might still experience deposition in a flood season with a higher sediment delivery ratio of the TGR.Moreover, there were more influences of the sediment delivery regulation on the Upper Jingjiang reach; in general, the sediment delivery ratio of about 30% was basically the dividing point between the erosion and deposition of the Jingjiang reach during a flood season under the flow-sediment conditions in July 2018;during a flood season, deposition mainly happens in slow-flow areas on point bars and concave banks in curved reaches, but the main-flow zone still experiences erosion, which was positive for maintaining the elevation difference between shoals and channels.