Abstract: A robust approach based on μ synthesis is proposed on the analysis of a dynamic set AGC model and engineering practice in hot strip mill. Even thought there is perturbation in stiffness, the performance of the system with the approach satisfies the request all the time. By introducing the fictive uncertainty characterizing the system capability and the main loop theorem, the problem that design a controller to satisfy the performance request with the model perturbation inside is transformed into the robust stability problem of an augmented system. Compared with H_∞ method, this method is more effective because of its design target more really reflecting the control target. In the end, simulation with the practical data proves the dynamic set AGC system with the method can achieve more robust performance than that of H_∞ method.