Concrete　filled　square　steel　tube　columns　with　very　large　sectional　sizes　are　widely　applied　in　recent　years.　However,　the　existing　axial　strength　models　of　concrete-filled　square　steel　tube　column　are　proposed　mostly　based　on　small　sectional　size　specimens.　Thus,　the　accuracy　of　existing　models　for　large　specimens,　viz　the　size　effect　of　these　models,　need　further　investigation.　In　this　work,　the　design　methods　to　calculate　the　axial　strength　of　concrete　filled　square　steel　tube　column　proposed　by　the　AIJ　code　of　Japan,　the　AISC　LRFD　design　specification　of　the　United　States,　the　EC4　code　of　Europe　and　Han　of　China　are　introduced.　Based　on　252　test　specimens,　the　comparisons　between　the　test　results　and　the　computational　results　by　different　design　methods　are　conducted.　It　can　be　concluded　from　the　comparison　that　the　design　methods　for　the　axial　strength　of　concrete　filled　square　steel　tube　columns　have　obvious　size　effects.　The　existing　design　models　may　overestimate　the　strength　of　the　specimens　with　large　sectional　size.　By　introducing　the　size　effect　model　of　concrete,　the　design　methods　are　modified　and　the　predicted　results　are　obviously　improved.　This　method　considering　size　effect　may　provide　a　reference　on　calculating　the　axial　strength　of　concrete　filled　square　steel　tube　columns　with　large　size.