In recent years, research has shown that as a good strategy for energy dissipation of spillway in stepped spillway have been considered. The design goals of stepped spillway can be used to increase the intensity of energy dissipation during spillway and thus reduce the dimensions mentioned stilling basin. Therefore optimum design of spillway on maximum energy dissipated main goal in this research. The dimensions of the spillway is considered as variables based on differential evolution algorithm and Firefly algorithm and also the combination of two algorithms for optimum design is variables. By increasing the flow rate is reduced relative energy dissipation and optimum height of the steps increases. In this study, three different inlet flow 422 (m³/s), 560.2 (m³/s), and 776.9 (m³/s), were used. The results showed that, for example, in  three  flow the energy dissipation during the horizontal steps of 200 meters by combining the algorithm, respectively, for the three flow is 79.29%, 78.47% and 68.47%.