Abstract: In order to study the earthquake response characteristics of a long-span steel arch bridge and the formation position and development process of plastic hinges in the bridge under soil-pile interaction,Ansys FEM software was used to comparatively discuss the effects of layered soil on the pile foundation and upper structure in consideration of structural dynamic characteristics and earthquake response under two different boundary conditions at the bottom of the bridge,i.e.,foundation consolidation and pile-soil inter-action. The results showed that the soil-pile interaction model reflected the effect of soil characteristics on the structure and it could better reveal the structural dynamic characteristics compared with the consolidation model. Using this model, the natural vibration period of structure was protracted, the period of high-order vibration modes varied significantly, and the internal force response of every part was declined, while the displacement response was amplified. But considering the effect of boundary conditions, the general trend did not change. The plastic hinges emerged on one fourth of the main girders, the girder-arch joint parts and the bottom of piers, the bottom of piers yielded firstly, while the deformation of plastic-hinge zones was still controlled in a smaller range, and the plastic hinge did not emerge on the piles.