Abstract: The mechanism of AC-DC interaction is the premise of security and stability control decision of multi-infeed DC system under commutation failure. We review the research status of the interaction mechanism between commutation failure and synchronous power grid from following four aspects: the classification and mechanism of commutation failure, influencing factors of commutation failure, evaluation indexes of commutation failure, and risk assessment, and analyze the interaction influence of AC/DC power grid from the perspectives of DC-AC and AC-DC. Finally, the quantitative analysis method of AC-DC system based on trajectory dynamics and its application status are introduced. The feasibility of extending the commutation safety assessment method from single-HVDC systems to multi-infeed HVDC systems continuous commutation failure is analyzed with an example, and the key technical problems that should be solved in the follow-up study on the interaction mechanism between multi-infeed HVDC commutation failure and synchronous grid dynamic response are pointed out. The quantitative analysis method based on the extraction of the disturbance extinction angle trajectories can achieve quantitative evaluation of multi-infeed DC commutation safety and the interaction analysis between commutation safety and system stability. Subsequently, the adaptability of quantitative evaluation of voltage and frequency drop acceptability in multi-infeed DC commutation failure scenarios should be analyzed theoretically. In the multi-dimensional quantitative indicator space, the impact of complex dynamic responses at multiple time scales in synchronous power grids on the safety of multi-infeed DC commutation is investigated in detail, and the interaction mechanism between multi-infeed DC commutation failure and synchronous power grid dynamic response is revealed.