To　investigate　the　torsional　performance　of　reinforced　concrete　(RC)　columns　strengthened　with　carbon　fiber　reinforced　polymer　(CFRP)　sheets,　a　mechanical　analysis　model　was　established　using　a　three-dimensional　numerical　method.　The　model　considered　the　heterogeneity　of　concrete,　and　the　interactions　between　steel　bars/CFRP　sheets　and　concrete,　simultaneously.　The　validity　of　the　numerical　model　was　first　verified.　Subsequently,　pure　torsion　was　added　on　40　CFRP　sheet-strengthened　RC　columns　to　investigate　the　influences　of　the　fiber　ratio,　the　structure　size,　and　the　cross-section　shape　on　their　torsional　performance.　Results　showed　that　(1)　size　effect　can　be　observed　in　the　nominal　torsional　strength　of　both　square　and　circular　CFRP　sheet-strengthened　RC　columns;　(2)　the　size　effect　of　square　columns　was　stronger　than　circular　columns　due　to　weaker　confinement　effects　of　CFRP　sheets　on　the　square　columns;　(3)　the　addition　of　CFRP　sheets　can　simultaneously　improve　the　torsional　strength　and　weaken　the　size　effect,　which　is　beneficial　to　the　torsional　performance　of　the　column.　Moreover,　a　torsional　size　effect　law　was　proposed　to　predict　the　torsional　strength　of　CFRP　sheet-strengthened　RC　columns　based　on　current　simulation　results.