This paper proposes a new parity space approach to a fault detection for general systems with noises, actuator faults and sensor faults. The proposed parity space approach could be more systematic than existing approaches since an efficient numerical algorithm is utilized. In addition, since the system and measurement noises are accounted in the proposed approach, the parity space residual will be noise-suppressed. When there are no noises and faults are constant on the interval of parity space’s order, the residual for each fault is shown to be exactly equal to the corresponding fault. The proposed approach is specified to the digital filter structure for the amenability to hardware implementation.