Abstract: In view of problems of low-order harmonics in output voltage, needing filter and transformer with big volume and dynamic voltage balancing of series components of HVDC transmission system based on VSC, the paper proposed a design scheme of light HVDC transmission system based on MMC. It detailedly introduced implementation of control strategy according to built mathematic model of MMC-HDVC transmission system. The control strategy controls MMC-HDVC transmission system in term of device level and system level, which separately realize balance control of capacitor voltage of submodules and power decoupling control of the system. The simulation result validated feasibility and effectiveness of the system.