Abstract: A lower-order robust decoupler design method is developed, which perfectly tackles the interaction and directionality of a multivariable system. The design procedure is composed of two steps: first turn the requirement of robust performance of a closed-loop system into constraints on the decoupler's parameters, then let the decoupler approach these constraints, resulting in a lower-order controller. Simulations have demonstrated that the robust performance of the controller based on this method is similar to that of the μ-optimal controller, and is obviously superior to that of the internal model controller(IMC).