The invention discloses a time-delayed stability criterion conservative assessment method based on Lyapunov function analysis, a numerical computation method is adopted to analyze a Lyapunov function, and conservative quantitative assessment is performed on time-delayed stability criterion. On the basis of a time-delayed power system mathematical model, constituent item difference of a corresponding Lyapunov function of an existing LMI time-delayed stability criterion is analyzed, system trajectory simulation and Lyapunov function normalization are performed on the difference, the derivative of the result is taken, a criterion conservative assessment index is further provided, and a time-delayed stability criterion conservative assessment method is constructed. Four existing typical time-delayed stability criterions are utilized to verify the provided method in a scene of a single-machine infinite bus time delay system. According to the invention, a Lyapunov function expression is utilized to directly analyze inherent differences of stability criterions and estimate conservatism of the criterions, and the method provides support for seeking more scientific time-delayed stability criterion.