The　model　experiment　of　a　steel　tubular　arch　under　in-plane　non-symmetric　loads　is　reported.　It　shows　that　the　displacements　of　the　model　developed　rapidly　for　its　small　rigidity.　Moments　was　the　main　forces　in　the　model　during　the　whole　loading　procedure　and　the　geometric　influence　was　distinctly.　The　collapse　model　of　the　steel　tubular　arch　is　of　the　second　stability　problem,　in　which　the　material　nonlinear　influence　is　obvious.　When　the　structure　reached　the　ultimate　loads,　the　plasticity　was　distributed　in　large　zone.　The　redistribution　of　the　stress　is　sharply,　the　ultimate　strength　can　not　be　calculated　by　the　ultimate　state　method.　6figs,　1tab.,　6refs.