The basic equation of the finite volume method,FVM,is obtained using the divergence theorem after being integrated.In FVM the unstructured mesh is used to represent the computational domain.Firstly,the mass and momentum fluxes through each side of every cell are calculated according to the balance theory.Then the water elevation and depth-averaged velocity of each cell are obtained at the end of each time interval.Two-dimensional unsteady flow model is based on the finite volume method.One of the attractive features of this model is to treat the calculation of the mass and momentum flux across each side of elements as a local Riemann problem that is solved using the flux vector splitting scheme (FVS).In this paper,the flow of the Yangtze River reach in Jiangsu Province is simulated.The sample applications of this model have shown fairly satisfactory results.It is proved that FVM cooperated with FVS scheme is a high -resolution method.Additionally,according to the distribution peculiarity of the four characteristic moments,the maximal contamination zone of entire tide has been obtained.The relationship between the length of contamination zone and the pollutant load is derived respectively.