Abstract: Wide-area damping control has been suggested to enhance the dynamic performance of interconnected power system.But time delay brought by wide-area signal transmission has a significant impact on the critical modes of wide-area power system,and thus change the stability of closed-loop system.Thus,analysis on time delay variation trajectory of the critical modes is of great theoretical significance for wide-area damping control design to suppress inter-area low-frequency oscillations.Firstly,based on Pade approximation,this paper converts time-delay into state space expression and builds linear model of closed-loop power system including wide-area damping controller.Secondly,the relation model of time delay effect on the electromechanical mode of power system is bulit.Arnoldi method is employed to research the rules of influence of time delay on inter-area oscillation mode,local oscillation mode and time-delay control mode.The method is tested on two-area four-machine system and New England system,and the results illuminate the validity in resolving the influence law of time delay.