A simple 1-D mathematical dendritic river network model of high precision which could rapidly realize the coupling between flow velocity and pressure is built based on Saint-Venant equations. Finite element volume method is employed to discretize equations of continuity, and semi-implicit θ to discretize the water level gradient term of free-surface elevation. Moreover, Eulerian-Lagrangian method is adopted to solve the advection term, and prediction-correction method to decompose the sparse linear system of dendritic river network to several tridiagonal systems. The reach from Zhutuo to dam site of Three Gorges Project is taken as a case study. The model is calibrated and validated with measured historical data in 2005 and 2006, and the results demonstrate that the calculation errors of water level and discharge are generally within 10% and 5%, respectively. The results of mathematical model are in good accordance with measured data, indicating that the model is of high precision.In the single-core serial efficiency test,the model takes about 23.7 seconds to simulate the flow process of a year,which implies the real-time simulation of hydrodynamic process of dendritic river network in Three Georges reservoir area can be completed.