Based on a new crank-slider inertia vibration excitation device, a two-degree-of-freedom fatigue loading test system for wind turbine blades was designed. Aiming at the problem of vibration coupling during bi-directional fatigue loading, the dynamic model of wind turbine blade two-degree-of-freedom excitation fatigue loading system is established. On this basis, a simulation model is established to simulate the system coupling process, and the system coupling process and basic laws under the influence of excitation frequency and installation position are obtained. The experimental results provide a theoretical basis for the control method of the two-degree-of-freedom fatigue loading system, and also provide a reference for the fatigue test of wind turbine blades.