Abstract: The interconnected power system with the integration of wind farms faces the difficulties of accurate modeling, complex time-varying operation conditions, and large fluctuation of wind power output, which leads to the instability of the inter-area low-frequency oscillation damping performance of the traditional supplementary damping controller for doubly fed induction generator (DFIG). Therefore, this paper proposes a supplementary damping control method based on data-driven robust control to enhance the damping performance of the inter-area oscillation in power systems, utilizing the reactive power modulation capability of DFIG. First, based on dynamic linearization technology, a data-driven model with a pseudo gradient (PG) matrix is established, and an online parameter updating method is proposed to adapt to the change of system operation condition to improve the accuracy of the data-driven model. Then, the data-driven discrete second-order sliding mode surface is designed to generate the control law, effectively suppressing inter-area oscillations while mitigating the adverse impacts of disturbances on the damping performance of the controller. Finally, the stability of the closed-loop system is analytically proved. The simulation results show that the proposed damping control method can effectively suppress the inter-area low-frequency oscillation under varying operating conditions and disturbances, thus significantly improving the adaptability and robustness of the control system.