HEC-RAS model is an one-dimensional hydrodynamic software from oversea which can simulate single river channel and complex dendritic or cyclic river network system involved in bridges, gates and pumps. Starting from the basic framework of the model, the principles, composition and main purposes of HEC-RAS was introduced in this paper, with its application in flood control evaluation illustrated through project case, and the rationality of the HEC-RAS model was verified by the MIKE11 model.