Abstract: Grid-forming converters have the ability to actively construct the grid, which can provide damping and frequency support for the power grid, but there are stability issues in low-impedance power grids. In order to study the stability mechanism of power synchronization control for grid-forming converters with low impedance, firstly, a small-signal model of grid-forming converters connected to the AC power grid that reflects the dynamic characteristics of power synchronization is established. Then, within the framework of Newtonian dynamics, a dynamic model of grid-forming converters connected to the low-impedance power grid is established by taking power synchronization control as the main method and the power offset is decomposed into synchronous and damping components to characterize the stability of the power synchronization control. Subsequently, by combining modal analysis and dynamic characteristic analysis, the influence of power grid strength and control parameters on power synchronization control is analyzed by studying the characteristic root trajectory and participation factor curves, as well as the changes in damping and synchronization components, and their underlying mechanisms are revealed. Finally, the conclusion is verified through a simulation model of grid-forming converters connected to the power grid.