The　addition　of　nano-silica　to　ultra-high-performance　concrete　(UHPC)　to　increase　its　toughness　has　been　proposed　to　obtain　ultra-high-performance　nano-concrete　(UHPNC).　This　work　mainly　studies　the　reinforcement　effect　of　UHPNC　on　concrete　filled　steel　tube　(CFST)　columns　under　long-term　load.　Ten　CFST　columns　strengthened　with　UHPNC　were　selected　and　reinforced　with　UHPNC.　The　influences　of　different　thicknesses　of　UHPNC　reinforcement　layer　and　different　nano-silica　contents　on　the　axial　compression　properties　of　specimens　were　mainly　studied,　by　loading　specimens　in　two　steps:　long-term　load　and　ultimate　load.　This　study　discussed　the　failure　modes,　compressive　toughness,　ultimate　bearing　capacity,　initial　stiffness,　and　ductility　coefficient　of　the　specimens.　The　results　show　that　the　outsourced　UHPNC　reinforcement　method　is　an　effective　method　to　improve　the　performance　of　CFST　columns　during　service　period.　With　the　increase　in　the　thickness　of　UHPNC　reinforced　layer,　the　ultimate　bearing　capacity　of　CFST　column　increases　greatly.　The　compression　toughness　is　increased　with　the　increase　in　nano-silica　content　and　UHPNC　reinforcement　layer　thickness.　The　decrease　rate　of　initial　stiffness　increases　with　the　increase　in　nano-silica　content.　　©　2023　the　author(s),　published　by　De　Gruyter.