A 3-D finite element model for Yueyang Dongting Lake bridge was established with a large scale general finite element analysis software, and the subspace iteration method was adopted to analyze the natural vibration characteristics of the bridge, meanwhile, the influences of settings different types of central buckles at the mid-span of the main spans between the main cables and girder on the dynamic behaviors of the long-span suspension bridge with deck-truss composite stiffening girder were studied. The results show that compared with only setting short hanger cable at mid-span, the the whole rigidity of suspension bridge is raised and the natural frequencies increase by the setting central buckle, but various types of vibration modes are affected in different extents; among all of these vibration modes, the antisymmetric vibration and Longitudinal floating of stiffening girder are most obviously affected. The stiffness of central buckle has a great influence on the vibration of main cable, while compared with only setting short hanger cable, the vibration of main cable increases 7.32% while setting the rigid central buckle. The conclusions of this paper provide theoretical basis for the using of central buckle in long-span suspension bridge.