A stepped spillway is a hydraulic structure, which is an integrated part of the dam, which allows the safe passage of overtopping flows. In this paper, experimental and numerical studies were carried out to investigate the effect different relative step height of spillways to get the best of dissipating the energy. Modelings of flow over spillway were carried out using a commercially available 3-D CFD model, FLOW-3D, which solves the RANS (Reynolds Averaged Navier-Stokes) equation. FLOW-3D was employed to analyze and obtain energy dissipation rate. The best geometry of the steps, through which the maximum energy dissipation can be achieved, was determined by reviewing related literature and inventing the proposed model in FLOW-3D.from resulting showed to the bets relative step height of spillways (hs/H) = 0.25.and the numerical models using FLOW-3D were found to be agreed well with the measured data for different experimental models.