In　order　to　study　the　effect　of　tube　rigidity　on　the　mechanical　character　of　truss　CFST　(concrete　filled　steel　tubular)　arch　bridge,　a　true　arch　bridge　was　taken　as　sample,　and　the　parameter　analysis　for　the　rigidity　was　carried　out　by　using　finite　element　model.　Based　on　the　investigation　of　section　composition　for　arch　rib,　a　suggestion　was　presented　to　calculate　tube　rigidity,　in　which　the　rigidity　reduced　factor　of　concrete　was　adopted　as　1.0　or　0.　4　for　different　calculation　demands.　Analysis　result　indicates　that　for　internal　force,　the　rate　of　calculation　value　to　reality　value　is　between　1.　2　and　1.　5,　for　deformation　the　rate　is　between　1.　5　and　1.　9.　So,　the　suggestion　can　secure　some　safety　reserve　for　the　design　of　truss　CFST　arch　bridge.