In order to more accurately study the transient voltage characteristics of Static Var Generator (SVG) during system network switching, a new electromechanical transient model is established in this paper. First, based on the basic equations of SVG with feedforward decoupling strategy, a feedforward voltage compensation method with first-order inertia link is proposed. Then, by ignoring the dynamic characteristics of phase-locked loop and DC voltage, an electromechanical transient model which can accurately reflect the instantaneous voltage characteristics of SVG is derived. The model no longer has pure current source characteristics, but introduces voltage source characteristics to a certain extent. Finally, the electromechanical transient model was established and simulated using the user-defined model under the PSASP platform. The simulation results show that the model is correct and effective, which is of great significance for accurately analyzing the transient overvoltage problem of new energy collection system with SVG.