Abstract: The virtual synchronous generator improves the inertia level and inertia support capacity of the renewable energy generation system by simulating the external characteristics of the conventional synchronous generator. However, the virtual synchronous generator also has the problem of power low-frequency oscillation of the conventional synchronous generator. This paper studies the mechanism of low-frequency oscillation in the parallel system of multiple virtual synchronous generators. First,the single-generator equivalent model of the parallel system of multiple virtual synchronous generators is established, and the mathematical expression of the equivalent model is deduced. Then, the analytical expression of the low-frequency oscillation frequency portrayed by active and reactive components is established. Furthermore, more the parameter influencing the oscillation frequency of reactive power is analyzed in terms of sensitivity to achieve the order reduction of the model. The influence laws of system parameters and control parameters on the oscillation frequency are revealed. Finally, the effectiveness of the model and the correctness of the theoretical analysis are verified by the simulation and experiments.