The axial load of a steel column will increase because of the axial restraint.Buckling of axial-restrained columns may occur at a lower temperature than that of free columns.But the steel column can still keep working after buckling in a fire for the axial load would reduce after the release of the axial temperature expansion.A rotational restrained steel column is converted into a hinge-support one by using the effective length coefficient

and a simplified calculation method for critical temperature of restrained steel column is proposed.The simplified calculation method can transform the axial restrained column into an unrestrained one by using an axial force amplification factor

and then the critical temperature of the restrained column can be obtained by the design method for unrestrained columns.The simplified calculation method is verified by an ABAQUS model.The critical temperatures predicated by the two methods agree well.