The invention discloses a modular multi-level converter configuration method and a modulation strategy thereof. Aiming at the problems of too many sub-modules in HVDC distribution network, the technical scheme adopted by the invention is as follows: a modular multilevel converter includes different level sub-modules, the high-level sub-module adopts IGBT which can withstand high voltage level, andthe rated voltage of the high-level sub-module is Uc1. Assuming the DC inter-pole voltage is Udc, the number of the high-level sub-modules N1 and the rated voltage of the low-level sub-modules of each bridge arm are calculated without considering the redundancy of the sub-modules. Modular multi-level converter modulation strategy with different level sub-modules adopts nearest-neighbor approximation strategy, and high-level sub-modules and low-level sub-modules adopt complementary differentiation method. The invention can reduce the total number of sub-modules, thereby reducing the investmentcost of the MMC and reducing the occupied area of the MMC on the premise of meeting the system requirements, especially the harmonic requirements.