The flush air data system(FADS) gets low accuracy during high altitude flight, which can easily fail if the vehicle travel through the atmosphere. Therefore, a calculation method for air data based on inertial navigation system(INS) and flight control system(FCS) is proposed. On the base of the aerodynamic model, force equations, and moment equations, the mathematic relationship between INS and air data is established. Real-time estimation of air data is achieved by using EKF. The simulation results show that, this method not only has high precision, favorable stability and robustness, but also improves the measurement range and reliability of the air data system, which can effectively be used to measure the angle of attack, the angle of sideslip and true airspeed within full flight envelope.