This　paper　suggests　a　separated　core　tube　flange　connection　column　joint　to　ensure　the　horizontal　shear　per-formance　of　box　section　steel　columns　at　the　flange　connection　to　meet　the　performance　requirements　of　column　-to-column　connection　in　high-rise　buildings　and　the　effective　connection　of　steel　columns　at　the　joints.　Low　cycle　reciprocating　loading　tests　were　conducted　on　three　specimens　with　different　parameters　(separated　core　tube　and　stiffeners)　to　study　the　seismic　mechanical　performance　of　the　connection　and　the　finite　element　analysis　(FEA)　of　separated　core　tube　column　connection　joint　was　performed.　The　result　of　the　experimental　study　shows　that　the　separated　core　tube　connection　joints　have　fuller　hysteresis　curves　and　higher　energy　dissipation　per-formance,　as　well　as　less　high-strength　bolt　tension　at　the　same　interlayer　displacement　angle.　This　investigation　provides　experimental　evidence　of　the　deformation　compatibility　of　the　separated　core　tube　connection.　The　mechanical　properties　of　the　separated　core　tube　connection　is　basically　the　same　as　that　of　the　welded　connection,　which　can　realize　the　rigid　connection　of　the　steel　box　section　column.　According　to　the　numerical　simulation,　the　failure　mode　and　mechanism　of　the　connection　were　obtained.　Based　on　the　results　of　tests　and　the　finite　element　numerical　model,　further　analysis　to　the　rotational　performance　of　the　separated　core　tube　flange　connection　joint　in　elasto-plastic　phase　and　yield-hardening　phase　is　carried　out,　and　a　three-stage　bearing　capacity　calculation　theory　of　the　joint　in　the　seismic　process　is　proposed,　which　was　verified　by　the　test　and　FEA.