Taking the 2180m double-layer steel truss suspension bridge, the Shiziyang Bridge, as the research object, the multiple strips method is used to analyze the seismic vulnerability of the structure in this paper. The material strain and curvature ductility are chosen as seismic damage performance indices. The relationship between the damage levels of bridge towers, cables, and other components and structural response is established. The probability of damage and failure of the Shiziyang Bridge under different seismic intensities is clarified. The research results show that the probability of damage and failure in the transverse direction of the Shiziyang Bridge is greater than that in the longitudinal direction. Structural damage occurs only when the peak acceleration exceeds 0.5g, while the peak design acceleration at the Shiziyang Bridge site is 0.21g, which indicates that the structure will not be damaged, and the overall seismic safety redundancy of the structure is relatively high.