Abstract: Soft open point(SOP) technology can effectively improve the power quality of distribution network and enhance the level of new energy consumption. At present, the voltage and current decoupling control method based on the rotating coordinate system is widely used in the modular multilevel converter(MMC) in the distribution system based on SOP. However, this control method is difficult to meet the performance requirements of the MMC converter in the flexible interconnection system under three-phase asymmetry, line fault and transient conditions. Therefore, according to the operation characteristics of multi-terminal flexible interconnection system, this paper proposes a unified direct control strategy of MMC based on multi-terminal flexible interconnection system. This strategy unifies the generation mode of current loop reference and simplifies the control strategy. Switching current loop reference is used to speed up the switching speed of MMC operating mode under multiple working conditions. The generation mode of bridge arm voltage reference is redefined to optimize the dynamic performance of MMC device. The reliability and effectiveness of the proposed control strategy are verified by simulation.