Abstract: In order to meet the inertia and damping requirements of grid-connected high-permeability new energy sources, virtual synchronous generator（VSG） technology was proposed. However, when the reference power or load is disturbed, it is easy to cause transient power circulation and power frequency oscillation between VSGs. But the above problems is difficult to fully describe through the existing small signal analysis model. Accordingly, the rotor dynamic model of synchronous generator was analogized to mechanical network by using electromechanical analogy principle, and then a torque-frequency dynamic modeling method was proposed based on mechanical admittance method. The mechanical admittance model of a single SG/VSG was established, which was further extended to a mechanical admittance model of multiple SGs/VSGs connected in parallel. In the model, the circuit theory was applied to analyze the power frequency characteristics of the system. It can not only give a detailed expression of the response characteristics, but also has certain applicability to inverters with different control strategies. The simulation results verify the accuracy and effectiveness of the model and theoretical analysis.