Time-delay is one of the reasons accounting for the instability of the power system in the increasingly complex power system. A tentative discussion has been made of the effect of time delay on the stability of power system. In view of the classical model of single machine infinite bus system in power system, the system equation affecting the time delay can be obtained through modeling, followed by the acquisition of the delay margin stability of the excitation control system by using the delay dependent stability condition based on the free weight matrix integral inequality. Finally, the actual model verifies the efficiency of the proposed method in the improvement of the delay margin of power system stability analysis.