Abstract: Froude number is an key parameter in open channel flows, but its systematic research of flows over stepped spillways is lacking. This paper presents a relative Froude number concept for stepped spillways by comparing their Froude numbers with those of the corresponding smooth chutes. We have conducted experimental tests of fifteen sets on a model stepped spillway using four different channel slopes (26.57°, 32.01°, 38.66° and 51.3°) and different step heights (0.5~2.0 m). Analysis of the test data shows that for a smooth-bottom chute, the Froude number of its non-uniform flow section takes good linear relations with flow length, unit width discharge, step height, slope, and relative energy dissipation head, while for a stepped spillway, the relations are complicated and difficult to apply. This experiment proves the necessity of stepped spillway analysis adopting relative Froude number.