An analysis has been made of the stability of a wide-area power system with time-varying delay. First, a wide-area power system model with time-varying delay is to be established, followed by the construction of a new L-K functional. Then, by introducing a quadratic function with respect to time-varying delay, a more conservative stability criterion can be obtained through integral inequality of the wide area power system with time-varying delay. Finally, the typical second-order system and four machine eleven bus system are simulated on Matlab, with the results compared with the results of other literatures, thus verifying the feasibility and superiority of the currently proposed method.