Abstract: Aiming at the non-negligible impact of time-delay on the stable operation of large-scale interconnected power system,this paper investigates the stability problem of power system with the influence of interval time-varying delay. Firstly, fully considering the influence of delay derivative on the stable region of power system, a new Lyapunov functional with delaydependent matrix is constructed. Then, new integral inequality is used to deal with the integral terms after delay segmentation in the analytical process, and the less conservative stability criterion with less variables is obtained, which expands the stable operation region of the power system. Finally, simulations of typical second-order time-delay system, single-machine infinite system, two-area four-machine system and load frequency control system are given to illustrate the effectiveness of the proposed method.