Abstract: A fault detection and diagnosis algorithm has been designed for flush air data sensing system,which is used by reusable launch vehicle.Parity check is adopted to fault detection.The number of parity equation is reduced by rough intensive reduction algorithm.After the reduction,the decision-making table is converted into rules.The rules reasoning process is based on the bit-vector logic judgment.The simulation shows that the diagnostic conclusion is accurate and reliable.Furthermore,the algorithm proposed can meet the real-time requirements of online diagnosis because of its fast computational speed.