An　improved　method　for　calculating　the　vortex-induced　vibration　(VIV)　of　bridges　is　proposed　in　this　article.　In　this　method,　the　nonlinear　characteristics　of　the　additional　aeroelastic　effects　during　VIV　versus　structural　amplitude　are　first　identified　through　an　instantaneous　identification　method　and　polynomial　fitting.　The　expression　for　the　aeroelastic　effects　as　a　function　of　structural　amplitude　is　then　transformed　to　the　function　of　structural　velocity　and/or　displacement　to　calculate　the　limit-cycle　oscillation　of　the　deck.　The　proposed　method　was　validated　through　an　experiment　with　different　mass-damping　conditions.　The　results　indicate　that　the　generalized　polynomial　model　with　parameters　identified　on　one　particular　mass-damping　condition　can　be　used　to　calculate　the　VIV　response　of　the　deck　within　a　certain　range　of　mass-damping　values.　Based　on　this　method,　the　VIV　performance　of　a　real　bridge　was　calculated　by　considering　the　influences　of　modal　shape　and　spatial　coherence　of　VIV　forces.　Compared　with　the　traditional　method,　the　applicability　of　which　is　limited　to　a　particular　mass-damping　condition　for　which　the　model　parameters　were　estimated,　the　proposed　method　will　significantly　reduce　the　uncertainty　in　the　prediction　of　the　VIV　performance　of　a　real　bridge.　(C)　2017　American　Society　of　Civil　Engineers.