The　performance　based　design　for　structures　should　be　based　on　the　theory　of　probability;　thus　establishing　a　reasonable　probabilistic　seismic　demand　model　of　structures　is　very　important.　This　paper　aims　at　the　regular　girder　bridges　of　highway.　8　representative　samples　are　built　by　OpenSees　software　and　the　time　history　analyses　are　carried　out　with　the　selected　2390　earthquake　records　at　three　different　site　conditions　by　cloud　approach.　The　spectral　acceleration　at　the　fundamental　period　with　5%　damping　(Sa)　is　selected　as　the　ground　motion　intensity　measure　and　the　displacement　drift　ratio　at　the　top　of　pier　(D)　is　selected　as　the　engineering　demand　parameter.　The　probability　distribution　between　Sa　and　D　for　different　bridge　samples　is　obtained　at　three　different　site　conditions.　The　result　shows　that　the　EDP　follows　an　approximate　lognormal　distribution　with　different　level　of　IM　at　three　different　site　conditions;　the　relevant　simplified　probabilistic　seismic　demand　model　is　built　by　the　analysis　results.　Example　of　verification　shows　that　the　simplified　probabilistic　seismic　demand　model　has　a　high　calculation　accuracy　to　simplify　the　calculation　of　probabilistic　seismic　demand　for　regular　bridges.　©　2016,　Engineering　Mechanics　Press.　All　right　reserved.