Aimed at the nonlinear MIMO system of electric power steering system, the nonlinear dynamic model of this system was established. Considering of the model error, H-/spl infin/ robust controller was obtained based on S/T method. Using mixed weighted sensitivity method, sensitivity function and complementary sensitivity function were designed. The simulation results show that the designed controller is proper. The closed loop system has better robust stability and can reject sensor noise and road perturbation effectively.