Test　of　six　specimens　of　concrete　filled　steel　tubular(CFST)　directly-welded　K-joint　was　carried　out.　Web　thickness　and　stud　welded　on　chord　inside　surface　were　chosen　as　the　parameters.　Axial　forces　were　equally　and　synchronously　applied　to　web　members　in　tension　and　compression　using　specially　designed　hydraulic　jack　and　connection　equipment.　It　was　shown　from　the　test　results　that　the　mode　of　joint　failure　was　influenced　by　the　wall　thickness　of　the　web　tube.　For　specimens　with　thin-walled　web,　web　in　compression　would　locally　buckle　near　the　connection　to　chord　tube,　while　for　specimens　with　thick-walled　web,　tear-out　failure　of　chord　tube　would　occur　around　connection　due　to　the　forces　of　the　web　in　tension.　Filled　concrete　in　chord　tube　could　prevent　CFST　K-joint　from　plastic　failure　and　punch　failure　of　chord　tube　under　web＇s　compressed　forces,　and　obviously　increase　the　ultimate　bearing　capacity　and　rigidity　of　the　joint.　Shear　studs　inside　chord　tube　would　not　change　the　failure　mode,　but　could　improve　the　transition　of　the　internal　forces　on　the　interface　between　chord　tube　and　the　concrete　filled　inside,　thus　increase　the　ultimate　bearing　capacity　and　rigidity　of　the　joint.　A　formula　was　proposed　for　predicting　the　ultimate　bearing　capacity　of　CFST　directly-welded　joint.