Abstract: For a class of multi-input multi-output (MIMO) hydraulic looper uncertain system in hot strip mills, a sliding mode controller was designed. First, the original uncertain system was turned into a standard model based on a particular linear transformation. Then, the sliding mode surface function was obtained by applying Lyapunov function approach and the linear matrix inequality (LMI) technique, and a novel sliding mode control (SMC) strategy was proposed and theoretically proved based on the sliding mode reaching conditions. Simulation results demonstrated that the proposed algorithm get much better control performance, and make the looper system come to a stable equilibrium state quickly. What's more, the control accuracy for looper system of hot strip finishing mills was also improved. This kind of control action has robust performance for looper and tension, which is suitable for the complex looper systems.