Abstarct: During the past two decades, modern dynamic systems have become very complex with large number of components and functional units. However occurring a fault is unavoidable. Faults can cause serious damage and make systems to become totally failure. Hence investigators pay attention to design safety and reliable systems. Fault detection system is a first step for fault tolerant system. The presence of model uncertainty, disturbance and noise is a main problem in practical fault detection systems since these uncertainties have the same effect as fault on fault identification signal (residual).distinguish between the effects of uncertainties and fault on residual are too hard. The design of fault detection system that is insensitive to uncertainty and at the same time to be sensitive to faults is called Robust Fault Detection systems. Generation of robust residual signal is a main purpose in fault detection system. Fault detection systems make decision on this signal. Designing fault detection filter by parity equation with H2/H∞ standard is provided in this dissertation. Simulation results on Boeing 747 aircraft illustrate high speed of this filter, good sensitive to fault, minimum sensitivity to disturbance and good response to any fault models.