The　main　span　of　Lanxi　bridge　on　Anxi　county　in　Fujian　province　is　down　-　bearing　concrete　-　filled　-　steel　-　tube(CFST)　rigid　-　framed　tied　arch.　This　kind　of　structure　not　only　has　the　advantage　of　convenient　to　build　as　a　fixed　arch,　but　also　economics　the　substructure　for　its　tie　rods　and　its　design　calculation.　The　structure　inner　-　forces　and　its　out　-　surface　elastic　stability　are　calculated　by　space　finite　elements　program　of　SAP93.　The　inner　-　surface　stability　bearing　capacity　is　checked　by　a　simplified　method　that　the　arch　is　set　as　a　simple　CFST　column.　The　tie　robs　and　hanger　robs　are　checked　referring　to　the　cable　of　cable　-　stayed　bridge.　The　main　point　of　construction　is　also　introduced　in　this　paper.