The concept of the modified edge and equivalent edge currents（EECs）by the modified edge representation are intreduced. and they are applied to calculate bistatic RCS of obects. A rule to determine the direction of the modified edge is presented based on the geometrical thoory of diffraction （GTD）

which is not considered as an empirical one. EECs by the medified edge only use the modified edge and the classical keller’s diffraction coefficients to obtain EECx out of the keller

and they overcome the ambiguity about definition of EECs at general edge points except for diffraction points. Numerical results show that the rule presented in this paper is reasonable

and that EECs by the modified edge representation posses high accuracy and do not cause additional false singularities.