摘要：Increasing the robustness to the unknown uncertainty and simultaneously enhancing the sensibility to the faults is one of the important issues considered in the fault detection development. Considering the l2-gain of residual system, this paper deals the observer-based fault detection problem. By using of H∞ control theory,an lMI approach to design fault detection observer is given. A numerical example is used to illustrate the effectiveness of the proposed approach.