Abstract: The grid-forming converters based on DC voltage synchronization cannot only stabilize DC voltage but also realize the self-synchronization of converters. However, the interaction between DC voltage dynamics and control loops may cause lowfrequency oscillation of the system. To study the mechanism of low-frequency oscillation, the “active power-power angle” model for stability analysis is built with consideration of the DC voltage synchronization control loop and AC voltage loop. It is found that DC voltage synchronization introduces more phase lag compared with active power synchronization, while the AC voltage loop also introduces phase lag in the loop. As a result, the system loop gain has the-180° phase crossing in the low frequency range with a high magnitude, thereby triggering the low-frequency oscillation issues. Based on the analysis of the low-frequency oscillation mechanism, two phase compensation methods for DC voltage synchronization control are proposed. Through reshaping the system loop phase in the high-gain-amplitude area of the low-frequency range, the damping control and oscillation suppression in the low-frequency range can be realized. Finally, the simulation and the experiment verify the correctness of the theoretical analysis and the effectiveness of the proposed methods.