Abstract: Subsynchronous control interaction (SSCI) may be triggered when DFIG-based wind farms are connected to the grid via series-compensated capacitors, which seriously threatens the safe and stable operation of the system. Embedding notch filters into the DFIG converter controllers can mitigate SSCI effectively. However, the fixed-parameter notch filter is difficult to adapt to the time-varying frequency characteristic of the subsynchronous oscillation in the actual system. To address the issue, a time-varying subsynchronous oscillation mitigation strategy based on the improved adaptive notch filter for DFIG-based wind farms is proposed in this paper. First, effects on blocking the subsynchronous oscillation component are analyzed when the ANF is installed at different positions of the rotor-side converter (RSC), and the best installation location of the ANF is determined. Second, the overall control framework is designed, and the strategy for ANF center frequency updating based on measurement data is developed. Finally, considering multiple influential factors such as wind speed, number of wind turbines, reactive power output, grid topology, etc., the performance of the proposed control strategy in mitigating subsynchronous oscillations with time-varying frequency is verified. Compared with the existing methods, the proposed method is independent of the accurate mathematical model of the system and presents stronger robustness and adaptability.