Abstract: The seismic behavior of the under-supported high-speed steel tube concrete tied arch bridge is studied. The Xuhonghe Bridge of CFST Tied Arch Bridge on Xuzhou-Yancheng High-speed Railway Passenger Dedicated Line is the largest span continuous beam-arch bridge in the octave seismic zone. A full-bridge finite element model is established using the finite element analysis software Midas/Civil. The natural frequency and mode shape of the structure are obtained by modal analysis. El Centro wave is selected and amplitude-modulated, and Rayleigh damping is used for calculation. The dynamic time-history response analysis of the bridge under the basic seismic intensity and the rare earthquake intensity is obtained, and the deformation and internal force under different acceleration peaks are obtained. The research results show that the arch bridge is mainly composed of longitudinal bridge vibration, the longitudinal stiffness is small, and the three-way seismic performance of the bridge is relatively balanced. Under the action of seismic load, the maximum internal force of the arch rib generally occurs at the arch foot, and the arch foot is the most vulnerable joint. The deformation of the bridge under the action of seismic load is analyzed. The main beam is mainly composed of vertical deformation, and the arch rib is mainly lateral deformation. The arch bridge has good mechanical properties under earthquake action and can meet the specifications of strength and ductility.