Multi-VSG grid-connected system faces the risk of the power, frequency and voltage oscillation that threatens the security and stability of system. This chapter builds a \([P/Q]-[\omega/V]\) “admittance” model of multi-VSG grid-connected systems and analyzes the power, frequency and voltage oscillation of the system. The presented model reveals interaction between different VSGs and depicts the active/reactive power and frequency/voltage response of VSGs under input power reference and grid voltage/frequency disturbances. Besides, based on the model, the stability criterion of the system is obtained. The influence of key parameters on the power coupling and oscillation characteristics is analyzed. Finally, the correctness of the presented model is validated by the control-hardware-in-loop experiment results.