This paper takes a large-span suspension bridge in Fengjie County with a novel design space cable system and a main span of 800 m as the engineering background. Based on the seismic wave parameters provided in the construction site seismic safety evaluation report, the dynamic characteristics and seismic performance of the bridge are calculated and analyzed. The results show that: the vibration period of the space cable system suspension bridge structure is longer, and the main beam vibration occurs first; under the action of earthquake load, the mechanical performance of key parts of the bridge is good; the viscous damper can improve the longitudinal seismic response and The deformation effect of the expansion joints is very significant, which greatly reduces the transverse bridge bending moment suffered by the main tower.