Thyristor-Controlled Series Compensator (TCSC) is one of the electric power lines series compensators. TCSC increases transmission system capacity and improves system dynamic and voltage stability. Several controllers have been proposed, but most of them generally improve one of TCSC capabilities. In this paper a TCSC robust controller is designed based on Nonlinear Quantitative Feedback Theory (QFT). This controller improves both of small signal and transient stability of power system.