This paper investigates the system stability of fuzzy-model-based control system. An auxil-iary-state-driven fuzzy controller is proposed to deal with nonlinear systems. With a particular and sys-tematic design, the system stability of fuzzy control systems is implied by the auxiliary and error systems. Instead of studying the system stability of the fuzzy control systems directly, the system stability of the auxiliary system and the error model is investigated. Furthermore, the auxiliary system offers a favour-able property that some system parameters can be freely designed. As a result, except the feedback gains of the fuzzy controller, these freely designed parameters can also contribute themselves to relax stability conditions. Based on the Lyapunov-based approach, the stability and performance conditions in terms of linear matrix inequalities are derived. Simulation examples are given to illustrate the effec-tiveness and design procedure of the proposed ap-proach.