Abstract: Within the inelastic range， Euler’s formula becomes inapplicable. Engesser successively proposed the tangent modulus theory and the dual modulus theory to address the buckling behavior of axially compressed members in the inelastic region. Subsequent validation confirmed the validity of the tangent modulus theory. Accordingly， the critical stress for axially compressed members in the elastic region can be expressed by Euler’s formula， and that for the inelastic region by the Engesser formula. By introducing a safety factor， the column curve can be obtained. As China’s first steel structure design code， the Design Code for Steel Structures （TJ 17-74） adopts this methodology to derive its column curve. However， the relevant parameters are not theoretical steel strength values but are determined through experimental testing.