This　study　conducted　bending　tests　on　both　square　and　circular　concrete-filled　stainless-steel　tubes　(CFSSTs)　using　Acoustic　Emission　(AE)　technique.　The　research　analyzed　the　mechanical　properties,　failure　modes,　and　AE　characteristics　of　CFSST　under　different　steel　tube　thicknesses　and　concrete　strength　conditions.　Among　series　and　by　tracking　the　AE　wave　features　(rise　time,　AE　counts　and　energy),　three　damage　stages　are　depicted:　initial　cracking　onset　(Stage　I),　cracks　release　and　steel　tube-concrete　interfacial　debonding　on　the　tensile　zone　(Stage　II),　and　near　failure　cracks　saturation　and　growth　and　steel　tube-concrete　interfacial　debonding　on　the　compression　zone　(Stage　III).　Rise　time　and　RA-average　frequency　distributions　during　testing　pinpointed　the　damage　onset　and　modes　shift　for　different　types　of　CFSST.　Increasing　the　thickness　of　the　steel　tube　effectively　delays　structural　failure,　with　circular　steel　tubes　demonstrating　better　suppression　of　tube　buckling　and　debonding,　ultimately　exhibiting　a　predominant　mode-I　tensile　failure　mode.　This　study　provides　valuable　guidance　and　experience　for　the　effective　health　monitoring　of　CFSST　structures.