In recent years, the issue of the flood disaster into Huaihe river is becoming increasingly serious, which threatens the safety of the lives and property of people. However, flood retarding basin has important control over the evolution of flood water, so the research on influence of flood retarding basin on flood control is particularly important. In this paper, the hydrodynamics method is adopted to calculus the conflux of the motion of flow in the mainstream of Huaihe River to build a numerical water flow model. The model is applied to simulate and calculate the motion of water flow. Compared with the measured data, the results show that the tally of computation and observation is in a good agreement. The model can be applied in production practice via appropriate improvement. Meanwhile, this paper takes Huayuanhu flood storage area as an example to study the influence of some factors that play relatively important roles in the example of case. The flow calculation model can forecast and analyze future historical flood , which provides us with reliable data and technical support to control the disaster of flood.