After the construction of the Three Gorges Reservoir,the water and sediment conditions in the middle and lower reaches of the Yangtze River have changed.The hydrological and sediment boundary conditions of the four rivers in the south of Jingjiang River from the Yangtze River to Dongting Lake have changed accordingly.The three outlets have decreased by 23% compared with before the construction of the reservoir,and the sediment distribution has decreased by 88.8%.The three channels have generally changed from erosion and deposition balance to erosion,of which the Songxi River erosion accounts for 47%.The Songxi River channel continues to widen under the medium water level.The erosion of some branches,bends and transitional reaches is more intense,and the thalweg swings greatly,which hinders navigation due to the instability of the beach and trough.Aiming at the channel problems caused by the change of the relationship between the Yangtze River and Dongting Lake,based on the study of the new water and sediment conditions and evolution process after the construction of the Three Gorges Reservoir,the characteristics and trends of navigation obstruction and riverbed evolution are analyzed.The Songxi River channel is mainly based on dredging and beach protection,and the beach stabilization and channel stabilization are carried out in sections.Taking the typical Peijiachang reach as an example,the engineering scheme is formulated,and the model test is carried out to verify the treatment idea and scheme effect.The research results aim to provide reference for the channel management of similar rivers and lakes.