Abstract: This paper gives a method for obtaining approximately the eigenvalues and eigenvectors under the unsteady aerodynamic environment in arbitrady states, The method is valid for the motion with multi-degrees of freedom and extends the relationship between the decay rate of structural motion as well as the fictitious structural damping coefficients and frequencies in the V-g method as seen in some references.The calculated results show that the present method is satisfied in estimating the dynamic characteristics of aero-elastic system. Comparing with the p-k method, the augment state method and the graphical techniques, the advantage of the proposed method is its simpli city.