Design floods provide important bases for determining structure grades and operation strategies of water conservancy projects. In order to calculate the exact design flood hydrographs and reduce the smoothing complexity and the uncertainty of existing design flood calculation methods, a multi-objective equilibrium optimization (MOEO) method was proposed based on the idea of equilibrium optimization. According to this method, a design flood error vector was constructed based on the errors of the peak flow, interval flood volume and flood hydrograph shape, and then a corresponding equilibrium optimization function was established to resolve design flood hydrographs using the improved cuckoo search algorithm. The case study shows that the calculated design flood hydrograph by the MOEO method can satisfy the constraints of the peak flow and interval flood volume, as well as keep the shape of a typical hydrograph; the MOEO method gets rid of manual smoothing and penalty factor adjusting, which is not only user-friendly but also effectively reduces the complexity and uncertainty in calculating design floods. Therefore, the MOEO method can provide a new approach for the calculation of design floods.