The variation of aeroelastic system dynamics is treated as the change of time-varying aerodynamic loads over rotating wind turbine blade. An Adaptive Control scheme is introduced to suppress blade fluttering, caused by unsteady aerodynamic loads, with trailing-edge flap. The robustness and effectiveness of designed Adaptive Controller are shown by good simulation results. For stability analysis, the proposed Adaptive Stability Theorem is proved theoretically by Kalman-Yacubovic Lemma and also illustrated numerically by certain case.