The　objective　of　the　present　study　is　to　study　the　failure　and　size　effect　of　squared　concrete-filled　steel　tubular　(CFST)　columns　subjected　to　eccentric　loading.　To　model　the　failure　of　squared　CFST　stub　columns,　a　threedimensional　meso-scale　simulation　approach　taking　into　consideration　of　both　concrete　heterogeneity　and　the　concrete-steel　tube　interaction　was　established.　The　meso-scale　method　was　first　verified　by　comparing　the　simulation　results　with　the　available　test　ones.　The　verified　numerical　model　was　then　employed　to　perform　the　investigations　on　the　influence　of　load　eccentricity　ratio　ranging　from　0.1　to　0.9　and　confinement　effect　on　the　failure　mode　and　nominal　strength　of　squared　CFST　stub　columns　having　the　constant　slender　ratio　of　3.0　and　having　different　structural　sizes　(i.e.　200　mm,　400　mm,　and　800　mm).　The　simulation　results　indicate　that,　as　the　magnitude　of　the　eccentricity　increases,　the　failure　mode　of　squared　CFST　stub　columns　changes　from　brittle　compression-shear　failure　to　ductile　bending　failure,　making　the　size　effect　on　nominal　compressive　strength　be　weakened.　Moreover,　as　the　confinement　effect　described　by　confinement　coefficient　arises,　the　nominal　strength　as　well　as　the　ductility　of　CFST　columns　improve　and　the　corresponding　size　effect　is　also　weakened.　Finally,　a　simplified　model　of　axial　force-bending　moment　(N　-M)　interaction　curve　for　predicting　the　bearing　capacity　of　squared　CFST　stub　columns　was　proposed　considering　the　influence　of　structural　size,　which　can　provide　conservative　predictions　when　compared　to　the　simulated　results.