The simplification of numerical simulation and model design of truss stiffening girder of suspension bridge is widely concerned. Based on the results of dynamic characteristics analysis of truss stiffening girder, by adopting the principle of equal fundamental frequencies of vertical bending, horizontal bending, and torsion, a simplified method was proposed for the calculation of equivalent mass moment of inertia, equivalent bending stiffness, and equivalent torsional stiffness of uniform section Euler beam under different boundary conditions (cantilever and two-end fixed types). The method was applied to the equivalent analysis of a plate-truss stiffening girder suspension bridge with main span of 576 m. Results show that the dynamic equivalent method was effective. All methods based on equivalent Euler beam had the disadvantage of not considering the shear performance of truss girder. Longer truss girder was closer to pure bending Euler beam, and truss girder of cantilever type was closer to Euler beam than two-end fixed truss girder. It is suggested to select longer delicate truss girder and cantilever boundary condition for the calculation of equivalent Euler beam of truss girder in suspension bridge.