China's hydropower reserves is the first ranking in the world.In recent years,the development of hydropower is rapid,the economic benefits of small and medium hydropower projects are mostly concerned by investors,witch is the primary factor affecting investor's decisions.According to the actual annual operating cost and the design operating cost of the Dazhuang hydropower station,the paper analyzed the reasons of the operating costs change and the impacts of the project economic benifit.The results show tha...