In　order　to　analyze　buffeting　response　of　long-span　bridge　subject　to　gust　wind,　and　solve　the　problem　of　complexity　of　traditional　buffeting　analysis　method　in　which　the　generalized　mode-shape　is　corresponding　to　one　special　state　of　the　structure　in　space,　a　method　based　on　mode　shapes　of　orthogonal　DOF　(degree　of　freedom)　was　proposed　in　this　paper.　Based　on　dynamics　of　structure　and　wind　tunnel　experiment,　this　paper　derived　bridge＇s　buffeting　response　in　form　of　mode-shapes　of　orthogonal　DOF.　Every　mode-shape　of　orthogonal　DOF　could　be　expressed　by　one　DOF　of　structure.　According　to　the　principle　of　conservation　of　energy,　the　generalized　mode-shapes　were　instead　by　mode　shapes　of　orthogonal　DOF　which　simplified　the　buffeting　analysis,　and　the　concern　dynamic　responses　could　be　obtained　easily.　Finally,　the　above　method　was　used　to　calculate　buffeting　responses　of　a　three　span　suspension　bridge　with　main　span　of　800　m.　The　results　show　that　the　buffeting　responses　of　long-span　bridges　are　large　and　cannot　be　ignored　in　design.　©　2016,　Editorial　Department　of　Journal　of　Chang＇an　University　(Natural　Science　Edition).　All　right　reserved.