An improved delay-dependent stability criterion for power system with multiple time-delays is presented. In this method， a Lyapunov function is constructed based on Lyapunov-Krasovskii theory. To reduce the conservativeness of the method， some necessary slack variables are introduced to its derivative function. The derivative function is then expressed as a set of Linear Matrix Inequalities（LMI）， which can be solved by the LMI toolboxes. A typical two-dimensional time-delayed system and the WSCC 3-generator-9-bus system are employed in the case study. The results reveal the validity and effectiveness of the presented method.