Abstract: First,based on the dynamic vector method,the 10th-order state space model of the main circuit of the Modular Multilevel Converter（MMC）is established,and then based on the actual project,the inner loop control of voltage and current,the outer power loop control and the circulating current,the state space model of the MMC controller within the control. Considering the sampling and calculation delays in the control link,the Pade approximation method is used to linearize the nonlinear delay link,and the system state space model of the MMC converter and the weak grid connection with the delay is constructed. Based on the eigenvalue method,the resonance mode of the state space model is analyzed,and the mechanism of the actual MMC-HVDC project’s high-frequency resonance and the influence of the controller input and output delay on the stability are analyzed. The simulation examples verify the correctness of the MMC converter state-space model and high-frequency resonance mechanism analysis in this paper.