An Artificial Neural Network(ANN)-based observer failure detection method is presented,which uses ANN's self-learning ability instead of analytical computation of the obsever design to get the redundancy relationship of the system.In order to deal with the failure detection of model uncertainty system,the failure detection of the control system sensor of a given aeroengine has been simulated with the presented method.The simulation shows that this method not only has the advantage of the observer failure detection method,but also has no need for the precise model of system.It is useful to the failure detection of the model uncertainty system.