Abstract: Traditional renewable energy grid-connected inverters are vulnerable to harmonic oscillations and other interaction stability problems when they are connected to weak grids. Firstly, the small-signal sequence impedance model of the virtual synchronous generator（VSG） was built and the sequence impedance characteristics of the VSG and the traditional grid-connected inverter were compared and analyzed. The sequence impedance of the traditional grid-connected inverter is mainly capacitive in the middle-frequency area and the impedance amplitude is quite high. However, the sequence impedance of the VSG is generally inductive and the impedance amplitude is quite low,which is consistent with the impedance characteristics of the grid. Then, based on the sequence impedance model and the Nyquist stability criterion, the influence of weakness the grid,the parallel number of inverters and phase locked loop（PLL）bandwidth on the stability of the VSG and the traditional grid-connected inverter system was analyzed. The stability analysis results show that the traditional grid-connected inverter loses stability easily while the VSG still works well and with no PLL restriction under the weak grid condition or with large number of inverters connected to the grid. Therefore,the VSG is more suitable to achieve high penetration renewable energy generation in the weak grid than the traditionalgrid-connected inverter from the point of view of system stability. Finally, experiment results validated the analysis.