This paper proposes a second-order sliding mode-based damping controller of DFIG for interarea oscillations. The proposed damping control strategy aims to utilize the reactive power modulation ability of DFIG to stabilize the power system in the event of oscillations caused by disturbances. First, the proposed controller is derived based on a two-area power system, and then it is extended to multiarea power systems. Compared with the conventional damping controller, the proposed one is insensitive to modeling uncertainties and parameter variations. Given the wide variation of operation points, the proposed sliding mode-based damping controller demonstrates a better robustness than the conventional damping controller. Simulation results on a two-area power system and a 10-machine 39-bus power system with DFIG-based wind farm integration show the improvement on system performance in interarea oscillation damping and demonstrate the robustness of the proposed control scheme in a wide operation region.