Communication time delay is detrimental to power system stability and a main reason of the performance deterioration or failure for the control systems. The paper starts with modeling of the power system based on time-delay differential algebraic equations. A method based on an improved Integral Quadratic Constraints (IQC) is constructed to guarantee the stability and control of power system with time-delays. Compared with the original IQC method, this method utilizes IQC algorithm to confine the input and output of time-delayed states of power system. Besides, a combination of IQC method and dissipation inequality is proposed to design the IQCC (IQC controller), thus, the stability criterion is more conservative. A two-area four-machine power system is built to conduct the simulation based on the TSAT software of DSATOOLS. The simulation results indicate that the proposed method can effectively damp the oscillation and weak the impact of time-delay on stability of power system.