A　new　procedure　is　proposed　to　derive　the　analytical　fragility　models　of　simply　supported　highway　bridges　based　on　an　improved　response-surface　method.　By　considering　of　the　uncertainties　in　the　structural　and　material　properties　of　the　bridges,　the　bridge　samples　were　obtained　by　Plackett-Burman　design　method.　From　the　nonlinear　time　history　analysis　through　the　OpenSees　software,　several　parameters　that　affect　the　seismic　response　of　the　bridge　significantly　were　identified.　From　the　bridge　samples　obtained　by　using　the　central　composite　design　(CCD)　method　with　the　chosen　optimal　parameters　focused　on,　response　surface　models　under　different　PGA　levels　were　established　from　the　finite　element　models　with　respect　to　each　component＇s　response.　The　simply　supported　bridge　system　was　assumed　to　be　a　series　system　and　the　fragility　curve　was　obtained　by　Monte　Carlo　simulation　method.　From　the　same　bridge　samples,　fragility　curves　generated　by　means　of　incremental　dynamic　analysis　were　used　as　a　benchmark.　The　results　of　the　traditional　response　surface　method　and　the　improved　response　surface　method　were　compared　to　each　other.　It　is　found　that　the　improved　response　surface　function　could　efficiently　replace　the　complex　nonlinear　time　history　analysis　and　improve　the　efficiency　of　the　fragility　analysis.　These　resulting　fragility　curves　will　assist　the　users　to　identify　the　vulnerable　bridge　components　over　a　large　seismic　intensity　range　and　aid　the　bridge　management　decision-making　process　to　prioritize　the　seismic　strengthening　repairs.　Therefore,　it　is　comparatively　valuable　as　a　new　procedure　in　relevant　civil　engineering　applications.　©　2018,　Engineering　Mechanics　Press.　All　right　reserved.