With　the　concrete　filled　steel　tube　K-shaped　(CFST-K)　joint　taken　as　the　research　object,　full-scale　model　tests　and　solid　finite　element　analysis　on　seven　CFST-K　joints　and　one　steel　tube　K-shaped　(ST-K)　joint　were　carried　out.　The　applicability　of　existing　stress　concentration　factors　(SCF)　of　CFST-K　joints　was　analyzed.　Based　on　the　effect　of　concrete　constraint　in　tube　on　the　deformation　morphology　of　CFST-K　joints,　the　relief　coefficient　of　SCF　for　CFST-K　joint　was　proposed,　and　the　calculation　method　of　SCF　of　CFST-K　joints　considering　concrete　constraint　in　tube　was　derived　by　theoretical　analysis.　The　results　show　that　the　maximum　SCFs　of　CFST-K　joints　all　appear　in　the　position　of　the　intersecting　weld　between　branch　tube　in　tension　and　main　tube　near　the　crown　point　of　main　tube.　The　SCF　of　CFST-K　joints　is　positively　correlated　with　the　wall　thickness　ratio,　while　the　diameter-thickness　ratio　and　tube　diameter　ratio　have　little　influence　on　the　SCF　of　CFST-K　joints.　The　maximum　SCFs　of　CFST-K　and　ST-K　joints　are　3.　98　and　6.08,　respectively,　and　the　concrete　in　tube　can　reduce　the　SCF　of　CFST-K　joints　by　about　34.5%.　The　existing　calculation　methods　for　the　SCF　of　CFST-K　and　ST-K　joints　fail　to　fully　consider　the　influence　of　concrete　constraint　in　tube　on　the　SCF　of　CFST-K　joints,　and　fail　to　consider　the　coupling　relationship　between　geometric　parameters,　so　the　accuracies　of　the　SCF　of　CFST-K　joints　calculated　by　these　methods　are　generally　low.　With　the　proposed　method,　the　calculation　error　of　the　SCF　of　CFST-K　joint　can　be　reduced　from　58.　0%　to　19.　6%.　©　2022　Editorial　Office　of　China　Civil　Engineering　Journal.　All　rights　reserved.