Carbon　Fiber　Reinforced　Polymer　(CFRP)　has　been　widely　utilized　to　wrap　concrete　column　in　order　to　improve　the　axial　compressive　bearing　capacity.　In　this　study,　the　size　effect　of　CFRP-wrapped　square　concrete　columns　was　investigated　using　both　experimental　and　numerical　approaches.　A　total　of　30　geometrically-similar　CFRP-wrapped　concrete　columns　with　a　maximum　cross-sectional　width　of　600　mm　were　designed　and　tested　with　repeated　axial　compression.　The　influences　of　loading　type,　structural　size　and　reinforcement　configuration　on　the　failure　of　the　columns　were　explored　and　measured.　Moreover,　a　3D　meso-scale　simulation　approach　considering　the　influence　of　concrete　heterogeneity　and　CFRP-concrete　interactions　was　utilized　to　furtherly　investigate　the　size　effect　of　CFRP-wrapped　columns.　In　the　3D　meso-scale　simulations,　the　failure　of　columns　with　larger　structural　sizes　and　larger　CFRP　fiber　ratios　was　analyzed.　The　size　effect　on　the　nominal　compressive　strength　of　CFRP-wrapped　columns　was　examined　and　discussed　in　detail.　Finally,　an　updated　size　effect　law　(SEL)　was　established　to　describe　the　size　effect　in　CFRP-wrapped　concrete　columns.　The　updated　SEL　is　proved　to　be　reasonable,　which　shows　good　consistence　with　the　present　experimental　data　and　simulation　results.　©　2020　Elsevier　Ltd