In　order　to　investigate　the　impact　of　the　triangular-corner　gap　between　the　outer　steel　tube　and　the　core　concrete　on　the　axial　compression　behavior　of　square　concrete-filled　steel　tubular　(SCFST)　columns,　this　study　conducted　axial　compression　tests　on　117　SCFST　columns　and　three　reference　hollow　steel　tubes.　The　main　test　parameters　included　steel　tube　thickness,　concrete　strength,　side　length　of　the　triangular　gap,　and　axial　gap　depth.　The　test　results　revealed　four　typical　damage　modes　in　the　SCFST　columns　with　triangular-corner　gaps.　The　presence　of　the　gap　defect　had　a　significant　effect　on　the　ultimate　bearing　capacity　of　the　SCFST　columns,　causing　a　decrease　in　the　range　of　1.66　%–17.72　%　when　the　gap　ratio　ranged　from　0.45　%　to　12.50　%.　Moreover,　the　influence　of　the　gap　ratio　on　the　ductility　and　initial　stiffness　of　the　SCFST　with　triangular-corner　gaps　was　dependent　on　the　concrete　strength　and　the　steel　tube　thickness.　Finally,　a　simplified　formula　for　calculating　the　ultimate　bearing　capacity　of　SCFST　columns　with　triangular-corner　gaps　was　proposed　based　on　the　test　data　and　force　analysis.　The　maximum　error　between　the　theoretically　calculated　value　and　the　test　value　is　within　15　%.　©　2023