Abstract: Based on impedance analysis, this paper focuses on the circulation control of a modular multilevel converter (MMC) and conducts in-depth research on the stability impact of offshore wind farm integration based on a permanent magnetic synchronous generator (PMSG) through the MMC-HVDC system. Firstly, the impedance model of a flexible MMC-HVDC converter station and an offshore wind farm is built by harmonic linearization, and then the impedance model of PMSG-based wind farm integration through the MMC-HVDC system considering the frequency coupling effect is derived. Secondly, based on the impedance-based stability criterion, the influence of circulation control on MMC impedance and the MMC-HVDC system’s stability is revealed, and then an MMC impedance remodeling control based on the circulation link is proposed. Finally, the stability analysis and the impedance modeling method are verified by RT-LAB hardware in the loop real-time simulation system.