Abstract:Abstract: The expression of the unsteady aerodynamics in time domain or frequency domain is established based on Theodorsen theory. The expression with integration was converted into second order differential equation. The unsteady aerodynamics on the structure was regarded as the reinforcement of the mass matrix, stiffness matrix and damping matrix of the finite-element model of structure. The whole dynamic characteristics were reserved. The general finite-element software could be used to calculate the flutter boundary of the air-structure coupling model. The method is suitable for the aeroelastic problem with complex structure. The unsteady aerodynamics data getting from any numerical methods or experiments can be used to establish the unsteady aerodynamics model which makes the method applicable to different cases. The flutter boundary of high-aspect ratio wing is calculated.