Based on a triple-tower suspension bridge, the finite element model was established. Using nonlinear time-history analysis, the seismic responses of the suspension bridge under different stiffnesses of elastic cables between the tower and deck were calculated, and the influence of elastic cable on the seismic response of the suspension bridge was studied. The seismic response of the suspension bridge with the flexible central buckle was analyzed, and the result was compared with that without a central buckle. According to the seismic response characteristics, the elastic-plastic seismic mitigation device was taken as the central buckle. To investigate the influence of the elastic-plastic central buckle on the bridge,s seismic response, the seismic responses of the suspension bridge with different elastic-plastic central buckles were calculated. The seismic mitigation effectiveness of the long-span triple-tower bridge with different seismic mitigation systems was discussed. The results show that the elastic cables between the tower and deck are unfavorable to the seismic forces of the middle tower, the flexible central buckle is vulnerable to the suspension bridge under earthquake. The elastic-plastic device can be used as the suspension bridge central buckle. By installing the elastic-plastic central buckle, the longitudinal seismic displacement of the deck can be effectively controlled and the seismic forces of the tower can be improved. When the combination of elastic cables and the elastic-plastic central buckle was installed, the displacement of the suspension bridge is reduced more obviously, the adverse effect of the elastic cable on the middle tower can be mitigated. The seismic performance of the triple-tower suspension bridge can be effectively improved by the application of the elastic-plastic central buckle.