Static phase shijlers (SPS) have the abilities to optimize power flow and to improve transient stability of power systems. In this paper, improving transient stability of the power system using the static phase shifrer is considered.First, a nonlinear robust model of the power system including SPS is established. Then a Backstepping method is used to construct the storagefinction, and a disturbance attenuation controller in the sense of L2-gain is achieved consequently. The controller reflects the nonlinearity of the system and attenuates disturbances explicitly. Simulations have proved the effectiveness of the nonlinear disturbance attenuation controller.