Abstract: An analysis of interaction of thin-walled circular steel tube and filled concrete under axial compression is carried out. Acting force and stress-strain relationship between thin-walled steel tube and concrete is presented. An axially compressive thin-walled steel element on elastic foundation is adopted to deduce the critical stress and critical diameter to thickness ratio for circular steel tube in local buckling. It is found that the critical local buckling stress and diameter to thickness ratio of circular steel tube are considerably increased by the support of filled concrete. Calculation for short columns using Grade Q235 steel tube filled with Grade C30 concrete indicates that the critical diameter to thickness ratio of steel tubes is about 1700.