Under　the　action　of　earthquake,　concrete-filled　steel　tubular　(CFST)　columns　are　often　subjected　to　torsion　action　or　combined　action　of　compression-bending-shear-torsion.　The　existence　of　torque　will　aggravate　the　damage　of　CFST　columns.　In　order　to　study　the　pure　torsional　failure　and　size　effect　behavior　of　CFST　columns,　a　numerical　model　of　CFST　columns　on　pure　torsional　failure　was　established　by　using　the　three-dimensional　meso-scale　numerical　simulation　method,　considering　the　meso-heterogeneity　of　concrete　and　the　contact　between　steel　tube　and　concrete.　The　influence　of　structural　size,　confinement　coefficient　and　cross-sectional　shape　on　torsional　failure　of　CFST　columns　with　different　sizes　were　analyzed.Finally,　the　Bažant　size　effect　law　was　compared　and　revised,　and　the　formula　for　the　nominal　torsion　strength　in　the　full　size　range　was　proposed.　The　results　show　that:(1)　Pure　torsion　failures　of　plain　concrete　columns　show　significant　brittle　failure　characteristics,　while　pure　torsion　failures　of　CFST　columns　show　certain　ductile　failure　characteristics;　(2)　The　pure　torsion　failure　of　the　CFST　column　has　the　size　effect,　and　the　size　effect　of　the　square　columns　is　stronger　than　that　of　the　circular　columns;　(3)　Under　low　constraints　(use　confinement　coefficient　to　mark),　the　size　effect　of　the　pure　torsion　failure　of　the　CFST　column　is　more　obvious,　with　the　increase　of　the　confinement　coefficient,　the　size　effect　of　the　nominal　torsion　strength　is　weakened.　©　2023　Editorial　Board　of　Journal　of　Basic　Science　and.　All　rights　reserved.