Abstract: Taking the IEA 15 MW wind turbine blade as the research object, a dynamic model of the blade aeroelastic system was established to investigate the characteristics of the aeroelastic response at the rated tip-speed ratio, with particular focus on the multi-degree-of-freedom coupling behavior. Results show that at the rated tip-speed ratio, the wind turbine blade experiences flapwise-edgewise coupled bend-bend flutter. The flutter is maintained by aerodynamic work in the flapwise and edgewise degrees of freedom, with a noticeable coupling phenomenon in the development of instantaneous aerodynamic power in these directions. The torsional direction contributes almost no energy to the flutter, exhibiting only minimal aerodynamic power throughout the process. This is primarily due to the coupling characteristics of the blade structure, which undergoes forced vibration excited by the flapwise and edgewise motions.