Prestressed　corrugated　steel-concrete　(PCSC)　composite　girders　are　often　subjected　to　combined　bending　and　torsion　in　practice,　but　the　existing　theoretical　models　have　mainly　focused　on　pure　torsional　behavior.　Thus,　this　paper　proposed　a　modified　combined　action　softened　truss　model　(MCA-STM)　to　predict　the　flexural-torsional　coupling　behavior　and　failure　modes　of　PCSC　composite　girders.　The　equivalent　loading　and　nonlinear　equations　were　modified,　and　the　convergence　criteria　of　flexural　and　torsional　failure　were　established,　considering　the　structural　characteristics　of　PCSC　composite　girders.　A　new　optimized　algorithm　was　employed　to　solve　the　MCA-STM,　providing　a　more　efficient　and　numerically　stable　solution　procedure.　A　3D　finite　element　analysis　(FEA)　model　of　the　PCSC　composite　girder　was　established,　which　was　verified　by　comparing　the　available　test　results.　A　parametric　study　was　carried　out　based　on　the　verified　FEA　model　to　get　more　datasets　with　various　parameters,　and　the　results　were　compared　to　the　proposed　analytical　model.　The　curves　obtained　by　the　FEA　and　MCA-STM　are　in　good　agreement,　indicating　that　the　proposed　analytical　model　can　predict　the　full　flexuraltorsional　coupling　behavior　and　failure　modes　of　the　PCSC　composite　girders.