Based on unstructured triangular grid and Finite Volume Method, a flow and sediment evolution model in flood diversion and storage area is founded in this paper. One advantage is that the model grids can adapt to complicated boundary conditions well, and the terrain data of the computational domain are obtained quickly by using DEM numerical model interpolation technology. Another advantage is that the sediment transport and riverbed deformation can be simulated synchronously. Key techniques including grid partition, numerical separation, treatments of movable boundary and dry riverbed are studied and the corresponding processing methods are introduced. Furthermore, the model has been applied successfully to the simulation of flood diversion in 1954 in Jingjiang flood diversion and storage area. The calculated flood results can serve as reference for flood control policy  making and flood rescue, and the maximum erosion depth behind the flood diversion gate can provide reference for engineering design.