Abstract: The dynamic model of single inverted pendulum system with time delay is set up based on Newton's second law.The inverted pendulum controller is designed based on linear quadratic optimal control strategy.The time delay unit is approximated by first-order symmetric Pade' series.The critical stable value of time delay of the close-loop system is acquired according to Routh-Hurwitz stability criterion.The effectiveness of the presented approach is verified by simulation and is compared with PID control strategy.Performance of the optimal controller is better than that of the PID controller.The controller has good control effect in critical delay range.However,the dynamic performance is somewhat reduced comparing with the state without any time delay.