This paper presents a numerical study on the parametric effect of deformable trailing edge flap (DTEF) on the fatigue load of a large-scale wind turbine blade. Investigations were conducted within the operation regions II and III of the turbine, respectively. Results showed that, compared with the original collective pitch method, the control effectively reduced the fatigue load on blade and drive-chain components, and positively affected the generator power and pitch system as well. Furthermore, the performances were gradually improved with increasing DTEF spanwise location from the rotor center, spanwise and central chordwise length, and deflection angle range, except for the worse performance with increasing spanwise location to the blade tip within region II. It was found that the smart control altered the nature of the flow-blade interactions and changed the in-phased fluid-structure synchronization into anti-phased interaction at main load frequencies, thus significantly enhancing the damping of fluid-structure system and contributing to greatly attenuated fatigue load on both rotor and drive-chain components. These phenomena happened for all primary load frequencies within region III, due to less flow detachment under the effect of the pitching function, determining its superiority over region II in terms of the control performance. (C) 2014 Elsevier Ltd. All rights reserved.