The flexible multi-terminal HVDC based on MMC is an important development direction of HVDC. This paper researches the control and protection system of flexible HVDC based on MMC. It introduces one control strategy based on sub-module capacitor voltage optimization of balance control algorithm and provides the protection configuration of flexible HVDC system in detail. The key technical problems of protection including the strategy of valve side AC busbar differential protection and inverter area protection are researched further. And a specific solution strategy is provided. A multiterminal MMC-HVDC simulation test system is set up to examine control and protection strategy. Then it analyzes the fault simulation results of two-phase connected to ground in valve side AC busbar, and the short circuit in inverter up bridge arm. The research in this paper has important significance for the research and development of multiterminal MMC-HVDC project.