Abstract: Energy dissipation ratio of stepped spillway is gradually reduced as its unit discharge increases, and it involves various problems of operation under large unit discharges. Previous studies of stepped spillway have focused on step size, spillway slope, energy dissipation, and various other issues, but very few on how to optimize the shape and layout of spillway steps. This paper describes a new type of stepped spillway that uses flat rectangular step sides and plane layout shapes of alphabet "M" to overcome the problems of operation under large discharge. Numerical simulation method of turbulent flow is used to study the energy dissipation features of this new spillway. Results show that under large unit discharge, the M-shape stepped spillway can be aerated more fully and its negative pressure area on the top step faces is smaller. And its dissipation rate is higher, because vortices of various scales occur near the step faces, causing three-dimensional local flow patterns.