Abstract: With the increase of number and capacity of grid-connected renewable energy source, Multi-terminal direct current (MTDC) transmission system based on Modular Multilevel Converter (MMC) is becoming the developing trend of high voltage DC transmission system due to such advantages as small harmonic components of output voltage, low switching loss and more flexible and reliable transmission mode. Firstly, the basic principle of MMC is analyzed, and relative researches on its topology structure, mathematical model and parameters design of main circuit are elaborated. Secondly, the control strategies of MMC-HVDC are summarized. Finally, the coordination control methods and its engineering construction of VSC-MTDC are analyzed.