This paper studies the multi-terminal flexible fractional frequency transmission system, which can coordinate the power distribution between the supply side and the demand side under the background of large-capacity offshore wind power transmission, and reduce the wind curtailment rate. This paper will combine the actual scene of offshore wind power transmission, based on a possible multi-terminal flexible fractional frequency transmission system topology, summarizes the coordinated control schemes for the interconnection of different types of wind farms and M3C, and designs the multi-M3C voltage margin control strategy. Finally, a simulation model is built, and the feasibility and effectiveness of the proposed research control strategy are verified.