The　combination　of　steel　tube　and　core　concrete　can　be　strengthened　by　installing　studs　(internal　studs)　on　the　inner　wall　of　the　steel　tube　of　the　concrete　filled　steel　tube　(CFST)　member.　Taking　core　concrete　strength,　stud　diameter　and　length　as　the　main　parameters,　the　push-out　tests　of　8　CFST　specimens　with　studs　were　carried　out.　The　results　show　that　the　load-slip　curve　of　the　CFST　internal　stud　specimens　consists　of　four　stages:　elastic　stage,　elastoplastic　stage,　load　decreasing　stage　and　load　residual　stage.　When　the　stud　shear　failure　load　reaches　the　maximum,　the　concrete　does　not　appear　cracking　and　crushing　phenomenon.　The　core　concrete　in　the　tube　will　not　separate　from　the　steel　tube　during　the　core　concrete　being　pushed　out.　The　ultimate　slip　value　of　studs　in　CFST　specimen　decreases　with　the　increase　of　core　concrete　strength,　increases　with　the　increase　of　stud　diameter,　and　less　affected　by　the　length　of　studs.　Based　on　the　analysis　of　the　test　results,　a　formula　for　calculating　the　ultimate　slip　value　of　the　inner　studs　is　proposed.　©　The　Author(s),　under　exclusive　license　to　Springer　Nature　Switzerland　AG　2025.