With the large-scale and long-distance grid connection of offshore wind farms via MMC-HVDC, the operating characteristics of power systems have become more complex. The interaction between wind power generation equipment and the power system has caused new sub-synchronous oscillations, which seriously threaten the safety and stability of the power grid. Taking the offshore wind farms connected to the power grid via MMC-HVDC, this paper analyzes the mechanism of oscillation and proposes an adaptive robust control method of battery storage systems to suppress power oscillations. Finally, the effectiveness and robustness of the proposed control strategy are verified on the PSCAD simulation platform.