To　reveal　the　mechanism　by　which　internal　studs　enhance　the　fatigue　resistance　of　concrete-filled　steel　tubular　K-joints　(CFST　K-joints)　and　to　develop　a　method　for　calculating　the　stress　concentration　factor　(SCF)　of　CFST　K-joints　with　internal　studs　(CFST　KS-joints),　this　study　conducted　full-scale　specimen　fatigue　tests　on　CFST　K-joints　with　array-Arranged　and　circular-Arranged　internal　studs.　The　influence　of　internal　studs　on　the　fatigue　performance　of　CFST　K-joints　was　thoroughly　analyzed.　The　equivalent　wall　thickness　theory　was　introduced,　and　the　wall　thickness　correction　factor　was　derived.　A　highly　accurate　SCF　calculation　method　for　CFST　KS-joints　was　established.　The　research　results　indicate　that　the　arrangement　of　internal　studs　can　enhance　fatigue　life　by　100.6%　and　reduce　the　SCF　by　77.6%.　Furthermore,　the　efficiency　of　circular-Arranged　studs　is　approximately　twice　that　of　array-Arranged　studs.　When　the　undetermined　factors　mc　for　CFST　K-joints　with　array-Arranged　and　circular-Arranged　internal　studs　are　set　to　0.002　and　0.019,　respectively,　the　maximum　deviations　of　the　wall　thickness　correction　factor　a　are　only　7.98%　and　8.20%,　respectively.　Utilizing　the　equivalent　wall　thickness　theory,　SCF　calculation　methods　for　CFST　K-joints　with　array-Arranged　and　circular-Arranged　internal　studs　are　derived,　yielding　errors　of　less　than　19.6%　and　21.4%,　respectively.　©　ASCE.