A mathematical model and state equation of the electric power steering system were established. The compensatory controller was designed by utilizing linear quadratic Gaussian/ loop transfer recovery (LQG/LTR) theory aiming at getting rid of the uncertainties and noise of measurement for electric power steering system. The compensatory controller was simulated and the results show that torque undulation and noise of measurement are inhibited well, the system possesses good robustness with the LQG/LTR controller.