Based on structural model from the ground vibration test (GVT) and the structural response at sub-critical speed, the generalized aerodynamic force coefficient vector can be solved. Generalized structural coordinate vector is designed as the input and generalized aerodynamic force coefficient vector is designed as the output. Identification technique is utilized to construct the reduced order aerodynamic model. The aeroelastic model based on experimental results can be constructed by coupling structural equation and aerodynamic equation in state space. Analyzing the characteristics of aero-structure coupling system changing with the dynamic pressure, the flutter onset behaviors can be solved by eigenvalue method. Different from the traditional flutter prediction method which needs a series of sub-critical responses, this new method only need one response at sub-critical speeds to predict the flutter onset. The new method can greatly reduce the cost and risk of flutter flight test or wind tunnel experiment.