To　study　the　flexural　behavior　of　composite　girders　with　concrete-filled　steel　tubular　(CFST)　truss　chords　under　positive　and　negative　bending　moments,　model　tests,　and　theoretical　analysis　were　carried　out　to　investigate　the　evolution　of　their　flexural　behavior　and　the　flexural　bearing　capacity.　The　results　showed　that　the　web　members　and　joints　of　composite　girders　with　CFST　truss　chords　subjected　to　positive　and　negative　bending　moments　had　high　strength　and　rigidity,　which　ensured　that　joint　failures　did　not　occur　before　the　failure　of　the　entire　cross　section.　The　longitudinal　strains　along　the　member　axis　changed　linearly　along　the　cross-sectional　height,　which　confirmed　the　correctness　of　the　plane-section　assumption.　The　failure　mode　was　due　to　the　yield　of　the　steel　tube　used　in　the　chord　and　the　rebars　in　the　concrete　slab　under　positive　and　negative　bending　moments,　respectively.　The　contributions　of　the　web　members　to　the　flexural　bearing　capacity　under　positive　and　negative　bending　moments　were　12.5%　and　8.6%,　respectively.　Calculation　methods　considering　the　contributions　of　the　web　members　to　the　flexural　bearing　capacity　under　positive　and　negative　bending　moments　were　proposed.　The　deviation　between　the　results　of　the　proposed　calculation　methods　and　the　test　and　the　results　of　the　finite-element　parametric　studies　was　less　than　8.1%.