In nature, the water quality deterioration phenomenon of river, the Yangtze River, lakes, estuaries and port bay has become a highlight problem of water environment to our country. In the comprehensive management of water pollution of the environment, the hydrodynamic and water quality of movement, migration need to be mastered to predict and control the pollution. Therefore, it is quite important to establishment the hydrodynamic mode in arbitrary curve coordinate. This paper uses the boundary curve fitting method to simulate the natural river channel for the complex boundary, and to simulate the shallow water equations and the equations which are closed and linked simultaneously. A numerical method, ADI difference scheme, is used to discrete the equations, numerical calculating 2D shallow water equations in curvilinear coordinates. Take the De Vriend’s 1800 plane curve flume experiment model as example, the numerical simulation results in this paper is validated with the experimental results of De Vriend, which is quite satisfactory. This proves that the numerical method established in this paper are reliable and correct, and it will provide reasonable and feasible means of calculation for Natural River hydrodynamic with arbitrarily complex boundary.