To solve the universal low voltage ride-through problem of the offshore wind farm based on MMC-HVDC under unbalanced grid fault, a new control strategy by combining PI voltage outer loop and internal model current inner loop is proposed along with the auxiliary protection scheme. First, the performance characteristic of Modular Multilevel Converter (MMC) under unbalanced grid fault is analyzed, the mathematical mode of MMC in αβ two-phase static coordinate is established. Then, the system control strategy based on Internal Model Control (IMC) method is designed in the aforementioned coordinate to suppress negative sequence current, meanwhile, aimed at the busbar voltage rise problem caused by MMC current-limiting feature in the case of two-phase grounding fault, the system auxiliary protection scheme based on DC discharge circuit is developed. Finally, the simulation model is established in Matlab/Simulink under the unbalanced operating condition of one- and two-phase grounding fault. Results indicate that the proposed control strategy and auxiliary protection scheme can ensure the offshore wind farm based on MMC-HVDC to implement the low voltage ride-through running even under the unbalanced grid fault, the low voltage ride-through capability of offshore wind farm is improved effectively. This work is supported by National Natural Science Foundation of China (No. 61673164).