Wrapping　concrete　columns　with　Fiber　Reinforced　Polymer/Plastic　(FRP)　jackets　is　an　efficient　method　to　strengthen　its　ductility.　At　present,　the　studies　on　the　axial　compressive　behavior　of　FRP　confined　concrete　columns　are　mainly　based　on　the　tests　of　small-sized　specimens.　There　is　lack　of　studies　on　the　failure　of　large-sized　columns,　leading　to　the　fact　that　the　studies　on　the　failure　mechanism　and　mechanical　properties　of　large-sized　FRP　confined　concrete　members　are　still　insufficient.　In　the　present　study,　a　three-dimensional　numerical　model　is　established　for　the　simulation　of　the　failure　of　GFRP-confined　concrete　cylinder　having　different　structural　sizes,　considering　the　heterogeneity　of　concrete　and　the　interaction　between　GFRP　and　concrete.　The　meso-scale　numerical　method　was　verified　by　comparing　the　simulation　results　with　the　available　test　ones.　Moreover,　the　influences　of　structural　size　and　constraint　(described　by　volume　allocation　rate　of　GFRP)　on　the　failure　mechanism　and　failure　modes　of　concrete　columns　were　examined.　Also,　the　effect　of　constraint　on　the　nominal　compressive　strength　and　the　corresponding　size　effect　of　the　concrete　columns　was　quantitatively　studied.　Finally,　based　on　the　classic　size　effect　law　(SEL),　a　semi　empirical-semi　theoretical　formula　that　can　describe　the　influence　of　constraint　generated　by　GFRP　on　the　size　effect　of　GFRP-confined　concrete　columns　under　axial　compression　was　developed.　Relevant　experiments　and　simulation　results　confirm　the　rationality　of　the　formula.　©　2019,　China　Water　Power　Press.　All　right　reserved.