To　study　the　fatigue　performance　including　distribution　of　hot　spot　stress,　regularity　of　fatigue　crack　development　and　fatigue　failure　mode　of　circular　hollow　section　(CHS)　K-joint,　fatigue　test　on　full-scale　CHS　K-joint　model　was　conducted.　Variation　of　stress　around　the　intersection　weld,　initial　imperfection　and　fatigue　crack　were　monitored　by　gradient　strain　gauge　and　phased-array　ultrasonic　testing　system,　respectively,　and　slicing　detection　was　also　carried　out　on　CHS　K-joint　with　fatigue　crack.　Furthermore,　the　rationality　of　evaluation　on　fatigue　life　of　CHS　K-joint　was　also　studied　based　on　nominal　stress　and　hot　spot　stress,　respectively.　It　is　found　that　hot　spot　stress　of　CHS　K-joint　is　suitable　to　be　obtained　by　linear　extrapolation　according　to　gradient　stress　measured　by　gradient　strain　gauge.　The　location　of　the　maximum　hot　spot　stress　appears　on　the　crown　point　of　chord　and　tensile　brace　intersection　welding　seam　near　chord　intersecting　line.　The　maximum　deviation　of　saddle　points　on　both　sides　of　CHS　K-joint　is　6.64%,　namely　test　results　of　CHS　K-joint　is　hardly　affected　by　out-of-plane　bending　moment.　Locational,　quantitative　and　qualitative　analyses　on　initial　imperfection　and　fatigue　crack　can　be　achieved　by　phased-array　ultrasonic　testing　system.　Fatigue　crack　of　CHS　K-joint　belongs　to　opening　class　I　crack　by　slicing　observation.　Loading　cycles　corresponding　to　crack　initiation,　crack　propagation　and　joint　damage　are　0-2.291　million,　2.291-2.455　million　and　2.455-2.512　million,　respectively.　Fatigue　crack　firstly　derives　from　the　crown　point　of　chord　and　tensile　brace　intersection　welding　seam　near　chord　intersecting　line　with　the　maximum　hot　spot　stress,　namely,　the　fatigue　failure　of　CHS　K-joint　belongs　to　brittle　failure　in　the　elastic　range.　Due　to　higher　amplification　coefficients　within　nominal　stress　range,　the　evaluation　result　of　fatigue　life　on　CHS　K-joint　is　excessively　conservative.　As　for　the　method　adopting　hot　spot　stress,　the　evaluation　result　acquired　by　CIDECT　is　unsafety.　However,　the　evaluation　result　acquired　by　API　possesses　a　safty　factor　of　1.11.　In　summary,　API　is　suitable　to　be　adopted　as　evaluation　criteria　for　fatigue　life　of　CHS　K-joint　in　the　fatigue　test.　©　2020,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.