Abstract: In order to meet various interconnection requirements of distribution network, flexible multi-state switch (FMSS) has derived a variety of technical forms for interconnection applications. Multi-terminal FMSS is more economical and reliable than dual-terminal FMSS, and has become a research hotspot. Traditional droop control can absorb unbalanced power by changing DC side voltage, but the deviation of DC side voltage will affect the safe and reliable operation of the system. Aiming at the multi-terminal FMSS system modular multilevel converter (MMC), we propose an improved droop control strategy, which dynamically changes the reference value of DC voltage and droop gain in real time according to the active power ingestion of the converter, thus realizing the unbiased operation of DC voltage. It can not only avoid the overload of converter station, but also solve the problem of voltage deviation caused by unbalanced power absorption, and improve the stability of the system. In addition, due to the structural characteristics of MMC itself and the difficulty of PI parameter setting, the traditional current inner loop is changed into model predictive control, and a typical second-order Runge-Kutta method is used to discretize the equation of state, which improves the control accuracy. Finally, a four-terminal FMSS system model is designed based on MATLAB/Simulink simulation software to verify the feasibility and effectiveness of the proposed control strategy.