The operation and construction of the Three Gorges Reservoir has an important influence on the hydrodynamic force of the tributaries of the reservoir. In this paper, Daning tributary of the Three Gorges Reservoir was used as an example, based on the Delft3D model, to establish a two-dimensional hydrodynamic model of Dachang of Daning River to Changjiang Estuary. The hydrodynamic characteristics of the Daning River under high water level and low water level operation of the Three Gorges Reservoir were simulated, and the distribution of water flow in the simulation section of Daning River was obtained. The simulation results show that the overall flow velocity of Daning River area is slow, which is less than 0.04 m/s when the Three Gorges Reservoir runs in high and low water level. The flow velocity of backwater regions of Daning River is less than 0.01 m / s at low water level and less than 0.001 m / s at high water level, which is obviously characterized by lacustrine facies, The water self-purification ability is greatly weakened, which is prone to cause water bloom and affect the water quality of Daning river. Our results can provide support information for the management of the tributaries of the Three Gorges Reservoir area.