In this paper, an FEM （Finite Element Method） model is established for the main span of the bridge, with the main box arch and suspender members modeled by beam elements, truss members by truss elements, and the orthotropic steel deck by plate elements. The natural frequencies and mode shapes are acquired by the eigen-parameter analysis. By input of a typical earthquake excitation to the bridge system, the dynamic responses of the bridge, including the displacement and accelerations of the main joints of the structure, and the seismic forces and stresses of the key members, are calculated by the structural analysis program, based on which the main laws of the seismic responses of the bridge are summarized, and the safety of the structure is evaluated.
