Abstract: In view of the system high frequency resonance generated by VSC HVDC connected into the AC grid, the impedance frequency characteristics of the VSC HVDC converter and the AC outlet line are analyzed, and the converter impedance model and the AC system equivalent impedance model are established. The paper analyzes the negative resistance inductivity characteristic of the modular multi-level converter (MMC) in middle high frequency range, and proposes that the converter control circuit delay, feedforward voltage and cross-coupling term are the main factors causing the converter impedance change. Based on the above analysis, for the high-frequency resonances generated in the separate operation mode of the two converters, the method of suppressing high-frequency resonance with a first-order low-pass filter in the current control circuit improves the impedance characteristics of MMC converter, and makes the converter impedance frequency characteristics not meet the resonance condition. Using the PSCAD model of the Yu to E back-to-back soft interconnection grid project, The correctness of the proposed method is verified by the detailed electromagnetic transient simulation.