Abstract: Based on the study of the hydraulic characteristics of the aerated flows,the theoretical calculation of the aerated water depth and the energy dissipation rate is derived by using the momentum equation on the pre-aerator stepped spillway.The relationship of the aerated water depth and the energy dissipation rate with the step sizes can be obtained theoretically through the equation.The calculated results agree well with the experimental date and are applied to the practical projects.The results indicate that the pre-aerator stepped spillway has the advantage of the easy control of the concentration of the aeration near the bottom floor,ensuring the sufficient aerating of the high energy dissipation rate in the bottom area,and suitable for the project with large discharge rate.This study provides the theoretical and experimental basis for the extension of the earlier study of stepped spillway design.