The dynamical analysis is significant for the design of the flexible roll-die forming machine. A new method for dynamical analysis of electromechanical systems by energy principle is proposed in this paper. The mathematical expression of the energy in each part of the system is presented by theoretical analysis and mathematical deduction. The reaction torque in the process of roll-die forming are extracted by FEM, and the differential equation of the roll-die forming machine is solved by the method of Runge-Kutta. The designed roll-die forming machine with the analytical results performs the feasible experimental verification.