In this study, nonlinear uncertainty and actuator saturation characteristics are investigated with respect to the issue of reducing the load of a wind turbine drive train. A method of active disturbance rejection control (ADRC) with actuator saturation is proposed to reduce the load on a wind turbine drive chain when the wind speed is below the rated wind speed. A tracking differentiator is designed to arrange the transient process for the error of the torsional vibration angle of the control system. An extended state observer (ESO) is used to estimate the strong non-linearity and "unknown disturbance", and this is compensated by a linear controller in real time. The actuator saturation is applied to prevent over saturation of the actuator (generator) and thereby to protect the complete system. Both convergence of the extended state observer and stabilization of the closed-loop system are discussed in this article. Finally, simulation results are detailed to demonstrate the effectiveness and robustness of the proposed control method. (C) 2018 Elsevier Ltd. All rights reserved.