In the field of power electronic inverter control, the virtual synchronous generator (VSG) technology realized by simulating the synchronous characteristics of synchronous generator had been fully researched as the main means to improve the stability of power system in recent years. And the stability of the system grid frequency was improved by solving the problem of the inertia of the distributed energy (DG) gridconnected system. However, when the power grid strength changes, the original VSG control strategy could not maintain the system frequency stability. In order to further improve the effect of VSG on frequency stability, the frequency stability of VSG system when the strength of grid is changed on the basis of traditional VSG control strategy was analyzed, and studies the factors that affect the change of power intensity. It was suggested that the frequency stability can be improved by increasing the system inertia in VSG. Finally, the effectiveness of the proposed method was verified by MATLAB/Simulink simulation tool.