Spiral　spacing　effect　on　axial　compressive　behavior　of　reinforced　concrete　filled　steel　tube　(RCFST)　stub　column　is　experimentally　investigated　in　this　paper.　A　total　of　twenty　specimens　including　sixteen　square　RCFST　columns　and　four　benchmarked　conventional　square　concrete　filled　steel　tube　(CFST)　columns　are　fabricated　and　tested.　Test　variables　include　spiral　spacing　(spiral　ratio)　and　concrete　strength.　The　failure　modes,　load　versus　displacement　curves,　compressive　rigidity,　axial　compressive　strength,　and　ductility　of　the　specimens　are　obtained　and　analyzed.　Especially,　the　effect　of　spiral　spacing　on　axial　compressive　strength　and　ductility　is　investigated　and　discussed　in　detail.　Test　results　show　that　heavily　arranged　spirals　considerably　increase　the　ultimate　compressive　strength　but　lightly　arranged　spirals　have　no　obvious　effect　on　the　ultimate　strength.　In　practical　design,　the　effect　of　spirals　on　RCFST　column　strength　should　be　considered　only　when　spirals　are　heavily　arranged.　Spiral　spacing　has　a　considerable　effect　on　increasing　the　post-peak　ductility　of　RCFST　columns.　Decreasing　of　the　spiral　spacing　considerably　increases　the　post-peak　ductility　of　the　RCFSTs.　When　the　concrete　strength　increases,　ultimate　strength　increases　but　the　ductility　decreases,　due　to　the　brittleness　of　the　higher　strength　concrete.　Arranging　spirals,　even　with　a　rather　small　amount　of　spirals,　is　an　economical　and　easy　solution　for　improving　the　ductility　of　RCFST　columns　with　high-strength　concrete.　Ultimate　compressive　strengths　of　the　columns　are　calculated　according　to　the　codes　EC4　(2004),　GB　50936　(2014),　AU　(2008),　and　ACI　318　(2014).　The　ultimate　strength　of　RCFST　stub　columns　can　be　most　precisely　evaluated　using　standard　GB　50936　(2014)　considering　the　effect　of　spiral　confinement　on　core　concrete.