In　this　paper,　a　modified　damage　model　is　established　to　solve　the　non-convergence　problem　existing　in　the　Park-Ang　damage　index.　The　scatter　of　the　modified　damage　index　is　significantly　reduced　compared　to　the　original　Park-Ang　damage　index.　Then　the　finite　element　analysis　models　of　8　representative　regular　bridges　samples　were　established　with　the　main　parameters　variable　such　as　the　column　height.　The　total　19120　increment　dynamic　analysis　(IDA)　curves　were　obtained　by　using　the　IDA　method.　These　IDA　curves　are　expressed　in　terms　of　one　intensity　measure　(IM),　i.e.,　the　spectral　acceleration　at　the　fundamental　period　with　5%　damping,　and　one　engineering　demand　parameter　(EDP),　i.e.,　the　modified　Park-Ang　damage　index.　At　last,　the　probabilistic　seismic　demand　model　of　regular　bridges　was　established　by　using　probability　analysis　based　on　the　result　of　IDA　curves.　It　is　found　that　the　seismic　damage　demand　is　reasonably　standard　beta　distributed　at　given　IM　levels.　The　quadratic　equation　is　suitable　to　establish　the　correlation　between　the　mean　value　of　the　seismic　damage　demad　and　the　IM.　It　is　concluded　that　the　established　probabilistic　seismic　demand　model　is　suitable　for　3different　site　conditions　and　can　largely　simplify　the　computational　effort　of　seismic　demand　in　the　performance-　based　seismic　design　and　assessment　of　regular　bridges.