Most　of　the　available　experimental　research　on　Fiber　reinforced　polymer　(FRP)　confined　concrete　columns　focus　on　the　fully-confined　and　small-sized　ones,　while　there　are　few　studies　on　the　axial　compression　behavior　and　size　effect　of　FRP　ring-confined　concrete　columns.　In　this　study,　a　three-dimensional　mesoscopic　numerical　model　of　Carbon　Fiber　Reinforced　Polymer　(CFRP)　ring-confined　concrete　in　a　circular　column　was　established,　taking　into　account　the　heterogeneity　of　concrete　and　the　interaction　between　CFRP　and　concrete.　Based　on　the　meso-scale　simulation　method,　the　failure　of　a　total　of　36　columns　with　different　structural　sizes　(the　maximum　crosssectional　width　is　1000　mm)　were　simulated,　and　the　influences　of　FRP　volumetric　ratio　and　vertical　confinement　effectiveness　coefficient　on　axial　compression　behavior　and　size　effect　was　explored.　Moreover,　considering　the　influence　of　FRP　volumetric　ratio　and　vertical　confinement　effectiveness　coefficient,　a　semi-empirical　and　semi-theoretical　formula　for　describing　the　size　effect　on　compressive　strength　was　established　by　modifying　Baz?ant＇s　size　effect　law　for　concrete　materials,　and　it　is　suitable　for　fully-confined　and　partially-confined　concrete　columns.　The　accuracy　and　applicability　of　the　proposed　formula　was　verified　by　comparing　with　the　test　results　and　the　predicted　results.