Abstract: According to the characteristics of single-machine infinite power system with static synchronous compensator (STATCOM), a new nonlinear controller design method is proposed in this paper. Firstly, the fourth-order affine nonlinear mathematical model of this system is built, and the nonlinear controller is designed by using of SDM hybrid feedback linearization H_∞ method based on robust H_∞ control method. Then detail control parameters of controller are obtained by solving Riccati equations that are established by MATLAB Robust Control Toolboxes. In the end, it can be seen from comparison of simulation results that the controller has effectiveness and superiority on improving system transient stability.