The types of hillside flow, the scouring mechanism and evolution of the profile form are studied on the basis of turbulent mechanics and hillside hydrology theory. Some basic concepts of hillside dynamics and theoretical calculation method of hillside scouring are put forward. By the method, the scouring intensity can be estimated for naked or vegetation-covered surface from the formation causes. The works also provide a scientific base for designs of soil and water conservation projects and comprehensive control plan.