As a crucial factor for stability calculation of frames, the effective length factor is generally determined by the traditional approaches in most current design codes, but some assumptions imposed do not reflect the real frame buckling behaviors. In this paper modified approaches are proposed based on the change of some unreasonable assumptions of the traditional approaches mainly in two aspects. Firstly, the premise that all frame columns buckle simultaneously is changed into an individual column buckling mode in braced frames, or story buckling mode in both braced and unbraced frames. Secondly, actual distribution of axial forces of columns is taken into account, so that the stability functions of columns may not be identical. Moreover, approximate formulas for calculation of the effective length factor are obtained based on the modified approaches, by which a series of numerical analysis is carried out. Numerical analysis results demonstrate that the modified approaches improve the accuracy well compared with the traditional ones.