The Modular Multilevel Converter High Voltage Direct Current (MMC-HVDC) technology is extensively utilized in the power transmission industry. There are numerous power electronic components in the MMC-HVDC system. The traditional state-space approach will lead to a marked increase in computational complexity during the modeling process, and it is impossible to directly obtain the frequency-domain information of the system. As the impedance analysis method boasts advantages such as precision, applicability, simplicity and intuitiveness, impedance analysis for modeling and investigation is adopted. Firstly, mathematical models of the MMC-HVDC main circuit and control system under light load conditions are established. Secondly, their impedance models are established, and the effects of critical parameters are analyzed. Finally, PSCAD/EMTDC simulations are carried out for validation and comparison, further verifying the validity and accuracy of the proposed models. The outcomes of this research contribute to a theoretical basis for MMC-HVDC projects and are of great significance.