Based　on　the　proposed　nonlinear　finite　element　model　of　externally　pretressed　steel-concrete　composite　girders,　the　parameters　analysis　of　influence　on　the　moment-angle　curves　in　the　positive　moment　and　negative　moment　areas,　included　the　concrete　strength,　degree　of　shear　connection,　and　the　initial　effective　prestressing　of　external　tendons,　were　conducted　in　this　papers.　After　that,　the　simplified　calculation　models　of　the　ultimate　flexural　capacity　of　the　externally　prestressed　steel-concrete　composite　girders　under　the　positive　and　negative　moment　loading　were　proposed　respectively.　The　results　reveal　that　the　plastic　ultimate　theory　may　not　be　adapted　to　calculate　the　the　ultimate　flexural　capacity　of　externally　pretressed　steel-concrete　composite　girders.　The　proposed　simplified　calculation　models　can　predict　the　ultimate　flexural　capacity　very　well,　and　can　be　applied　to　the　engineering　design　of　externally　pretressed　steel-concrete　composite　girders.