Forecast of discharge parameters is one of the key problems needed to solve urgently for applications of electromagnetic forming technology (EMF). In this work, the forecast of discharge voltage for electromagnetic tube forming has been investigated through a combination of the sequential coupling numerical simulation of EMF process and the design optimization of tube deformation. The optimum design of tube deformation during EMF process is discussed. The relative error between the experimental value and the forecast one is less than 5.9%, which indicates that the discharge voltage forecast method is feasible. This forecast method will be a favorable way for the optimum design of electromagnetic sheet metal forming and tube forming with die.