The study on elasto-plastic analysis of framed structures based on the plastic hinge concept has been greatly developed by use of matrix method, and on the elasto-plastic in-plane instability problem of columns with pretty high axial force, a great deal of work has been done experimentally and also analytically, especially by CDC method. As to the elasto-plastic instability problem of columns subjected to high axial force and also hi-axial bending moments, several kinds of analytical method have been published. However, in most work, the kind of applied load is limited to eccentrically axial loading and more over the computation is complicated. In this paper, simplifying theory by neglected torsion effect and adopting a new concept with respect to bending stiffness of a section, a unified method for computing the elasto-plastic behaviour of columns subjected to axial force and also to bi-axial moments is proposed. Many kinds of column problems will be able to be solved by use of this method, for example, a column with initial deflection, bi-axial eccentricity and a column with loading-program. The computation results were compared with the experiments of four H -section columns with loading-program, and it showed that this method is useful to predict column behaviour in elasto-plastic range.