A sensor’s analytic reconfiguration control method is presented based on unknown input observer (UIO) for aero engine distributed control system（DCS） with control delay and unknown disturbance. An unknown input observer is in correspondence with a sensor whose input is a controlling quantity and information for other sensors, and output is a reconfiguration signal corresponded to the sensor in troubling. The existing sufficient condition of UIO, which is described by linear matrix inequalities, is deduced for small-divergence state space model of aero engine. When the gain of the controller is given, the parameter matrix of the UIO can be solved, and all the UIOs can be designed by iteration. The numerical simulation result shows that when the sensor is out of order, the UIO’s output may go instead of fault sensor’s signal as a state feedback value to control the engine model, and the system has a good dynamic response under different disturbance. This proves that the observer can decouple the external disturbance and not be influenced by the fault sensor and effectively reconstruct the fault sensor signal.