Abstract: A dynamic stability analysis approach to an airplane equipped with automatic-control systems is demonstrated in this paper. As this sort of stability problem is due to the interaction between auto-control systems and structural vibration modes, it can be regarded as a kind of servo-aeroela-sticity instability phenomenon and it can also be refered to as servoflut-ter in the case of flight.This paper introduces two technical approachs to solving the previous problems. The numerical calculation of a complete system including unsteady aerodynamic forces is presented. In order to observe the influnce of the control systems on the airplane flutter, results of both open and closed loop calculations are illustrated with Nyquist and V-G diagrams.The results of calculation indicate that servo-aeroelasticity problem should be highly regarded in the process of airplane design and it is necessary to select a suitable notch filter for the control systems.