A new modular multilevel converter topology is proposed in this paper. On the basis of traditional modular multilevel topology, a conventional sub module of each arm is replaced by 3 new sub modules, and the capacitance of the new sub module is 2 times of that of the conventional sub module capacitor. Then the corresponding control strategy is proposed. The capacitor voltage of the new sub module is half of the traditional sub module capacitor voltage, and the voltage level arm can be increased from N+1 to 2N+1. Besides, the improved Nearest Level Modulation strategy is adopted, the voltage level of the AC side phase is increased to 4N+1. Under the environment of MATLAB/Simulink, the system simulation model is built according to the topology and control strategy proposed in this paper. The simulation results show that this method can effectively reduce the cost of hardware and improve the quality of power supply in the case of MMC with a large number of sub modules.