This　paper　investigated　the　axial　compressive　behavior　of　concrete-filled　square　steel　tube　(CFSST)　columns　with　debonding　defects.　Experimental　tests　were　conducted　on　117　CFSST　columns　to　examine　the　influence　of　debonding　defects　on　their　failure　modes　and　performance　deterioration.　The　results　showed　that　pronounced　buckling　and　concrete　cracking　were　observed　at　the　debonding　interface　due　to　stress　concentration.　The　presence　of　debonding　defects　slightly　decreases　the　ultimate　load-carrying　capacity　of　CFSST　columns　but　more　significantly　deteriorates　the　ductility　and　initial　stiffness.　A　2.5　%　volume　debonding　rate　reduces　ultimate　load-carrying　capacity　by　11.8　%,　while　ductility　coefficient　and　initial　stiffness　by　27.4　%　and　38.1　%,　respectively.　Furthermore,　the　debonding-induced　imbalance　in　the　constraint　effect　of　the　steel　tube　significantly　contributes　to　the　performance　deterioration　of　CFSST　columns.　This　deterioration　is　more　severe　in　columns　with　concentrated　defects　compared　to　those　with　uniformly　dispersed　defects.　Finally,　a　theoretical　formula　was　proposed　to　accurately　predict　the　ultimate　load-carrying　capacity　of　CFSST　columns　with　debonding　defects.　This　formula　takes　into　account　the　deterioration　of　the　constraint　effect　caused　by　interfacial　debonding.　These　findings　inform　failure　and　deterioration　analysis　for　CFST　structures　with　debonding　issues.　©　2024