Abstract: The flow and sediment regime downstream of the Three Gorges Reservoir has been changed dramatically after impoundment of the reservoir. The fluvial processes of downstream channel reaches can be affected as a result of the change. In order to simulate the morphological changes in a long river section, a 2-D and 3-D coupled model for turbulent flow and sediment transport as well as bank erosion is developed. A new coupler is proposed for coupling of the 2-D and 3-D models on the basis of mass conservation for flow and sediment transport. The coupled model is tested on a 60 km long section of the middle Yangtze River for the period from October 1996 to October 1998. The result shows that the coupled model simulates well the alluvial channel migration processes, which demonstrates that the coupled model is able to provide an effective method to investigating the morphological changes in response to the changes of flow and sediment regime in the Jingjiang segment of the middle Yangtze River.