Grid power oscillation occurs when distributed generators connected to grid, the model of grid-connected inverter controlled by Virtual Synchronous Generator (VSG) is established, and its swing equation of VSG control is conducted using power circle model. The process to the linearization and independence of active and reactive power is realized by introducing gradient coefficient. The optimal second-order step response model of input power and output power is established, and the damping configuration method of linear independent VSG control swing equation is designed. When the damping ratio gets 0.707, the dynamic response to power oscillation in low frequency to steady state in the parallel power system gets optimal. The simulation results show that the proposed gradient coefficient and damping configuration are effective. This work is supported by Science and Technology Project of State Grid Corporation of China Headquarters (No. 080 and No.2015YF-56).