Abstract: Transonic unsteady aerodynamics model can be obtained by CFD/CSD couplingcomputation, but it is disadvantaged to analyze and integrate ASE problemsbecause of the high order of the model. The high order ASE model is dealtwith order reduction technique using system differentiate and analyses, andbalanced truncation in this paper, and to integrate with the low ordermodel. Outlines of this paper can be generalized as follow: (1) The unsteadyaerodynamics reduced-order model (ROM) is gained by applying Volterra seriestheory, and the aero-servo-elasticity (ASE) model is gained by couplingconfiguration dynamics and servo dynamics; (2) A lower ASE reduced-ordermodel is obtained using the balanced truncation method; (3) Based on ASEreduced-order model a mixed sensitivity H_\infty controller is designedfor flutter suppression to reduce the order of the controller while keepingits robustness. At last, in a typical BACT system, simulations of modelreduction and active flutter suppression controller designing are given. Theresult shows that the ASE reduced-order model based on ROM can reflectflutter characteristic of practical system factually, and it has lower orderthan CFD/CSD coupling model, while the low-order robust controller designedbased on balanced truncated ASE model can apply to practical systemeffectually, and increased the flutter speed by 36%.