Shitanxi　Bridge　is　a　concrete　filled　steel　tubular　(CFST)　half-through　arch　bridge.　The　suspended　longitudinal　RC　T-shaped　floor　beams　in　the　through　part　of　the　bridge　are　supported　on　the　PC　cross　beams　which　is　suspended　by　high　tensile　steel　cable　hangers　to　the　arch　ribs.　Such　a　deck　system　without　a　longitudinal　stiffening　girder　will　behave　large　deflection　and　vibration　because　of　its　bad　integrity　as　well　as　vertical　stiffness.　Therefore　in　order　to　improve　its　service　quality　and　risk　resistance　capacity,　a　strengthening　project　is　proposed　by　setting　longitudinal　steel　tubular　trusses　between　the　crossbeams.　The　static　and　dynamic　behavior　of　this　bridge　before　and　after　strengthening　are　analyzed　and　field　tests　both　for　static　and　dynamic　behavior　after　strengthening　were　carried　out.　Analysis　and　test　results　show　that　the　proposed　project　is　effective　on　improving　the　dynamic　performance　and　risk-resistance　capacity.　This　strengthening　method　is　not　only　economic　and　applicable,　but　also　has　little　influence　on　traffic　during　construction.