Modular multilevel converter （MMC） has many advantages such as stable operation and diversified control，precise modeling of which has become a current research hotspot. A complex vector-based impedance modeling method for MMC AC/DC side is proposed. According to the basic principle of complex vector modeling, the positive and negative sequence conversion relationship of converter is analyzed. Under the premise of considering the three-phase coupling, the modeling points of the three-phase MMC are briefly described from the perspective of differential common mode, and the complete time domain model of the three-phase system is established. The theory of harmonic state space （HSS） is introduced to process the model to improve the modeling accuracy, and the basic principle of interface matrix and impedance solution is introduced to complete the establishment of AC/DC impedance model of MMC. Finally, a comparison experiment is carried out on the simulation platform, which proves the feasibility of the modeling method.