A　method　to　analyze　the　dual　nonlinearity　behaviors　of　CFST　(single　tube)　arch　subjected　to　spatial　loads　is　presented.　Spatial　beam　element　is　used　in　the　finite　element　model.　The　fiber　element　model　is　used　for　the　normal　stress-strain　relation　and　the　standard　curve　in　the　unify　theory　of　CFST　is　used　for　the　shear　stress-strain　relation.　The　analyses　of　the　nonlinear　property　of　the　CFST　model　arches　both　with　a　single　rib　and　two　ribs　indicate　that　the　method　proposed　herein　can　get　out　the　basic　mechanic　behaviors　of　the　steel　tubular　CFST　arch　subjected　to　spatial　loads　on　the　whole　loading　progress.　Under　the　spatial　loads,　the　affection　of　the　geometric　nonlinearity　to　the　behaviors　of　CFST　arch　is　more　seriously　than　the　material　nonlinearity.　The　spatial　actions　of　the　CFST　arch　with　single　rib　is　obviously　great　than　that　with　double　ribs.