A MW wind turbine blade single fatigue loading system is designed. The vibration coupling mathematical model based on the Lagrange equation is established, and the numerical simulation of the vibration characteristics (blade amplitude, motor current) is obtained. When the deviation between the driving frequency and natural frequency of the blade is small, the electromechanical coupling phenomenon leads to the stability of the blade amplitude. If the deviation increases, the amplitude tends towards disorder. The current of the loading source follows the blade vibration fluctuation. At higher speeds, the current in the condition of the equivalent load is relatively large when the current reaches maximum resonance. Finally, a single-point fatigue loading test system is set up that measures the blade amplitude and motor current on the vibration process. Test results verify the accuracy of both the mathematical and simulation models. The above conclusions provide the theoretical basis for the fatigue loading control algorithm.