Abstract: For a single machine-infinite bus system with static synchronous compensator (STATCOM) of which the parameter uncertainty is involved under external disturbance, the problem of robust H∞ control is studied. Storage functions of control system are constructed on the basis of modified adaptive backstepping and Lyapunov methods, with a robust H∞ controller and the parameter substituting law designed simultaneously. With the fact that the damping coefficients are hard to measure accurately in the internal disturbance emphatically considered, the proposed controller is able to not only keep the nonlinearity of power system and the real-time parameter estimation but also constrain the influences of disturbance on system output. The simulation results verified the effectiveness and advantages of the proposed controller.