Abstract: As an efficient grid-connected inverter, modular multilevel converter (MMC) is widely used in renewable energy fields such as wind power generation and solar power generation. Aiming at the problems of slow response speed and inaccurate control accuracy of grid-connected system caused by the change of system parameters and working conditions, combined with the advantages of extended observer in estimating system state and disturbance, simplifying control algorithm design, improving system performance and robustness, a model-free current control of MMC based on extended observer is proposed, which can realize the estimation and control of system state by using the feedback information and data-driven method of the system. Firstly, the MMC topology is analyzed and its hyperlocal model is established. Then, the model-free current controller of MMC based on extended observer is designed, which retains the characteristics of simple structure and few tuning parameters of the model-free controller. Finally, the simulation is built. Compared with the traditional PI double closed-loop controller, the results show that the response speed and control accuracy of the proposed control strategy are better than those of the traditional PI control under dynamic and static conditions.