Abstract: The thickness and tension system in tandem cold rolling has the features such as multivariation,strong coupling and uncertainty.To improve its control accuracy and quality,a new robust control scheme based on the invariance-decoupling theory and H_∞ mixed sensitivity method was presented.First,a dynamic coupling model for the thickness and tension system was built,and the invariance-decoupling theory was applied to completely decouple the thickness and tension system.Then,for systematic uncertainty of modeling error,parameter perturbation and external disturbance,a robust controller was designed based on H_∞ mixed sensitivity method to ensure the robust stability and robust performance of the system.Simulation results show that the thickness and tension system after decoupling is controled better,proving the validity of the algorithm.