For a complex structure of multiple degrees of freedom (DOF), building a simplified model of equivalent structure can lead to rapid and effective structural analysis. The method of energy equivalence was used to make a long-straight complex structure of multiple DOF equivalent to a beam element in space, the stiffness and inertia characteristics of the equivalent beam were derived, and the total stiffness matrix and mass matrix were obtained by using the finite element method. For a wing model, using the equivalence method, stiffness values and inertia values of the equivalent beam had been gotten. Analysis of vibration and flutter was carried out, and their respective results were separately compared with the calculation results of MSC Nastran. The contrast shows that the equivalent modeling method significantly reduces the structural DOF, and that the relative errors of results are small. And its main parameter values can be conveniently modified. Therefore, the method can be applied to preliminary design and structural optimization design of aircraft.