Abstract: According to the characteristics of flow-sediment transport in the middle-lower reaches of the Yangtze River system,a numerical model is established with combination of the 1-D and 2-D unsteady flow and the sediment model to simulate the transport of the flow-sediment and the bed scouring silt ing processes of the middle-lower reaches of the Yangtze River,Dongting Lake and their network Some relevant problems are discussed,including the moving-boundary in the network,the computation patterns of flow-sediment diversion at channel bifurcations,the moving riverbed resistance and the exchange pattern of water-sediment among the rivers and the lake Based on the hydrologic and topographic data of the middle-lower reach of the Yangtze River,the model verification shows good results for the flow transport characterist ics and the riverbed variation patterns for the middle-lower reaches of the Yangtze River,Dongting Lake and their network.