This paper studies the evolution mechanism of concave scour and convex sedimentation of Chibakou waterway bend downstream the Three Gorge Reservoir under the new conditions of water and silt,and adopts the methods such as prototype observed data analysis,theoretical analysis and mathematical model to analyze the bend evolution mechanism.The results show that the water and sediment conditions changed by impoundment of Three Gorge Reservoir are the main influencing factors for bend evolution,and it is also predicted that the phenomenon of concave scour and convex sedimentation is likely to develop continuously.