Studies　on　buckling　of　steel　tubular　truss　arches　are　lacking　in　contrast　to　steel　arches　with　solid　web　sections,　although　they　have　been　widely　applied　in　long-span　structures.　This　paper　deals　with　the　in-plane　elasto-plastic　buckling　and　strength　design　of　circular　steel　tubular　truss　arches　with　triangular　sections　by　using　finite　element　analyses　(FEA).　Firstly,　the　in-plane　buckling　failure　modes　are　explored　to　reveal　the　buckling　mechanics　of　truss　arches.　By　introducing　the　normalized　slenderness　of　the　entire　arch　and　the　chord　tube,　as　well　as　the　interactive　coefficient　that　accounts　for　the　effect　of　chord　tube　buckling,　the　unified　buckling　curve　for　truss　arches　in　uniform　compression　are　obtained.　Lastly,　an　interactive　equation　is　proposed　for　in-plane　buckling　resistance　of　steel　tubular　truss　arches　under　combined　compressive　and　bending　actions.　It　is　found　that,　the　buckling　of　diagonal　web　tubes　greatly　reduces　the　load-carrying　capacity　and　deformation　ability　of　truss　arches　hence　should　be　prevented　in　design.　The　chord　tube　deformation　always　exists　during　the　buckling　failure　of　the　truss　arch　and　its　effect　on　the　buckling　resistance　is　inevitable.　The　buckling　curve　b　in　the　codes　can　used　for　truss　arches　in　uniform　compression,　and　the　interactive　equation　can　provide　satisfactory　lower　bound　predictions　for　truss　arches　under　general　loading.