Abstract: A robust fault detection scheme is proposed for a class of time delay systems with both unknown inputs and modeling uncertainties.The fault detection filter is designed by using H_∞ control theory.The robustness of the residual to uncertainty is proved and then linear matrix inequality(LMI)approach is used to derive the existence conditions of the robust fault detection filter(RFDF),which is independent of time delay.Finally,an example is given to demonstrate the effectiveness of the proposed approach.