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　interaction.　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.