A general aeroservoelastic model construction method based on CFD / CSD couple simulation is investigated. The aeroservoelastic system is divided into three parts including aerodynamic, structure and control subsystems whose state equations are built separately and then are integrated into an integral aeroservoelastic system model. The system identification method of the state equation of the unsteady aerodynamics is investigated, especially the identification of the impulse response. A simple moving mesh generation method and an improved CVT method exchanging data between aerodynamic grid and structure grid are applied in the CFD / CSD program. The comparison between the results of the state equation and the direct simulation indicates that the model obtained by this method is good in accuracy, easy in usability and high in efficiency.