A new design scheme of an emersed hydropower arch gate is presented based on topology optimization method. Three main components of the gate, i.e., two arms, a water-retaining face plate and its supporting frame, are considered in the present design method. Both of the layouts of the arms and the supporting frame are obtained by using topology optimization method instead of traditional experiments. In design process, firstly, the location, topology and shape of the arms of gate are obtained. Secondly, the layout of ribs in the support frame is found. Finally, the integrated structure is formed by using the components obtained above and the new gate satisfies such constraints as strength, stiffness and stability. The new gate is about 30% lighter than the one obtained by using traditional method, which means much material is saved and the new gate can be easier for operating.