Based　on　the　results　from　experimental　researches　and　dual　nonlinear　finite　element　analyses,　the　equivalent　beam-column　method　to　predict　the　plane　ultimate　load-carrying　capacity　of　the　CFST　(single)　rib　arch　is　proposed.　The　equivalent　lengths,　applied　forces　and　calculation　method　of　the　ultimate　load　of　CFST　are　analyzed.　Analysis　results　indicate:　It　is　better　to　calculate　the　strengths　of　CFST　beams　and　columns　by　using　Code　DL/T;　take　0.72　S　(the　arc　length　of　the　arch　axis)　as　the　equivalent　length　and　the　inner　forces　at　the　springing　section　as　the　acting　forces　when　the　arch　loads　are　asymmetrical;　take　0.62　S　(the　arch　length　of　the　arch　axis)　as　the　equivalent　length　and　the　inner　forces　at　the　crown　section　as　the　acting　forces　when　the　arch　loads　are　symmetrical.　Comparisons　with　the　dual-nonlinearity　finite　element　method　show　that　the　predicted　results　of　the　equivalent　beam-column　method　follows　the　basic　rule　of　the　ultimate　loads　of　the　CFST　(single)　rib　arch　and　they　may　be　referred　to　in　future　research　and　engineering　practice.