Concrete　filled　steel　tubular　(CFST)　composite　girder　is　a　new　type　of　structures　for　bridge　constructions.　The　existing　design　codes　cannot　be　used　to　predict　the　thermal　stress　in　the　CFST　truss　girder　structures　under　solar　radiation.　This　study　is　to　develop　the　temperature　gradient　curves　for　predicting　thermal　stress　of　the　structure　based　on　field　and　laboratory　monitoring　data.　An　in-field　testing　had　been　carried　out　on　Ganhaizi　Bridge　for　over　two　months.　Thermal　couples　were　installed　at　the　cross　section　of　the　CFST　truss　girder　and　the　continuous　data　was　collected　every　30　minutes.　A　typical　temperature　gradient　mode　was　then　extracted　by　comparing　temperature　distributions　at　different　times.　To　further　verify　the　temperature　gradient　mode　and　investigate　the　evolution　of　temperature　fields,　an　outdoor　experiment　was　conducted　on　a　1:　8　scale　bridge　model,　which　was　installed　with　both　thermal　couples　and　strain　gauges.　The　main　factors　including　solar　radiation　and　ambient　temperature　on　the　different　positions　were　studied.　Laboratory　results　were　consistent　with　that　from　the　in-field　data　and　temperature　gradient　curves　were　obtained　from　the　in-field　and　laboratory　data.　The　relationship　between　the　strain　difference　at　top　and　bottom　surfaces　of　the　concrete　deck　and　its　corresponding　temperature　change　was　also　obtained　and　a　method　based　on　curve　fitting　was　proposed　to　predict　the　thermal　strain　under　elevated　temperature.　The　thermal　stress　model　for　CFST　composite　girder　was　derived.　By　the　proposed　model,　the　thermal　stress　was　obtained　from　the　temperature　gradient　curves.　The　results　using　the　proposed　model　were　agreed　well　with　that　by　finite　element　modelling.