Abstract: Stepped spillways have attracted great interests of researchers to date. This paper describes a concept of relative velocity over a stepped spillway and compares its velocities with those over a corresponding smooth spillway to explore in depth the mean velocity and its related hydraulic performances. We have conducted an experiment testing four different chute slopes of 26.57°, 32.01°, 38.66°, and 51.3° at a step height range of 0.5m ~ 2.0m, and examined the relationships of cross-sectional mean velocity over steps and relative velocity versus flow path length on the stepped section, unit width discharge, step height, chute slope, and relative energy dissipation rate. The results show that the mean velocity over the steps of a stepped spillway has a complicated nonlinear relationship with flow length, unit discharge, and the dissipation rate, while relative velocity varies linearly with these parameters. Generally, relative velocity much depends on unit discharge, size of stepped spillways, and chute slope, increasing with step height and chute slope and decreasing with unit discharge. It also takes a good linear relationship with the dissipation rate. At a fixed relative dissipation rate, an increase in unit discharge causes a decrease in relative velocity, which means a lower flow resistance.