Abstract:MMC has been an important part of the HVDC engineering application all the time. Therefore, it is a great practical significance to study its control strategy. Based on the mathematical model of MMC in three-phase stationary coordinate system, a mathematical model in DQ rotating coordinate system is established. According to instantaneous power theory, MMC-HVDC system controller is designed for outer loop power and inner loop current. Aiming at the traditional capacitor voltage balancing strategy, an improved sub module capacitor voltage sharing method is proposed from the perspective of reducing switching frequency. Due to there are too many sub modules in the real model, the NLM strategy is adopted to make the system more stable and reliable. Finally, a 89 level MMC-HVDC system model is built in the Matlab/Simulink simulation software. From the angle of changing the reference value of the controller and the active power reversal , the control system is simulated and verified the reliability and stability of the MMC-HVDC system controller .