To　investigate　the　nonlinear　impact　effect　of　multispan　simply　supported　beam　bridges　under　strong　earthquakes,　firstly,　the　dynamic　motion　equation,　the　algorithm　of　its　solution,　and　some　pounding　modelling　methods　are　presented　and　the　finite　element　model　of　a　considered　multispan　simply　supported　railway　beam　bridge　is　established　in　the　nonlinear　finite　element　software　of　SAP2000　in　which　the　primary　nonlinear　characteristics　of　the　bearing　and　the　impact　element　are　considered　herein.　Secondly,　the　natural　vibration　characteristic　of　the　considered　railway　bridge　is　analyzed　to　prepare　for　the　subsequent　parameter　analysis.　Finally,　the　influence　of　three　nonlinear　parameters,　i.e.,　stiffness　of　impact　element,　separation　gap　width　of　expansion　joint,　and　bearing　stiffness,　on　impact　responses　of　bridge　structures　is　studied.　The　results　show　that　the　first　several　modes　of　multispan　simply　supported　beam　bridges　are　mainly　longitudinal　and　vertical　vibrations.　Under　longitudinal　seismic　excitations,　the　large　longitudinal　displacement　response　is　induced　possibly　and　results　in　the　collision　or　even　unseating　of　superstructures　at　the　expansion　joints　and　abutments.　The　influence　of　separation　gap　width　between　adjacent　decks　on　the　pounding　effect　of　bridges　is　greater　than　that　of　collision　stiffness　originated　from　the　pounding　modelling　element.　The　impact　force　and　pounding　number　run　up　to　the　maximum　conditional　on　the　collision　stiffness　of　9.9x10(9)　(N/m)　and　the　separation　gap　width　of　0.14　(m).　The　bearing　stiffness　affects　significantly　the　displacement　of　the　pier　top　and　the　cross-sectional　internal　force　at　the　bottom　of　piers　but　has　little　effect　on　the　collision　force　and　number.