The　probabilistic　seismic　demand　models　of　structures　are　key　parts　of　realizing　seismic　design　of　engineering　structures　on　the　basis　of　probability　and　performance.　The　probabilistic　seismic　demands　of　8　representative　regular　highway　bridge　samples　are　derived　using　increment　dynamic　analysis　(IDA)　method　by　selected　2390　earthquake　records　at　three　different　site　conditions.　The　probability　distributions　of　three　engineering　demand　parameters　(EDP):　the　pier　top　drift　ratio,　displacement　ductility　and　normalized　hysteretic　energy　are　established　at　different　intensity　measure　(IM),　the　spectral　acceleration　at　the　fundamental　period　with　5%　damping,　levels.　It　is　found　that　the　selected　EDPs　are　reasonably　lognormal　distributed　at　different　IM　levels.　A　practical　probabilistic　seismic　demand　model　based　on　the　pier　top　drift　ratio　is　proposed　by　using　the　regression　analysis　method.　The　practical　probabilistic　seismic　demand　model　is　suitable　for　three　different　site　conditions,　and　can　greatly　simplify　the　calculation　of　seismic　demand　in　the　probability-based　and　performance-based　seismic　design　of　regular　bridges.