The virtual synchronous generator (VSG) has attracted much attention due to its ability to improve damping and inertia in the power grid. When the line presents a high impedance ratio and a large power angle, there is a serious power coupling problem between the VSG output active and reactive power. Based on a feedforward compensation strategy, an adaptive feedforward compensation control strategy is proposed. First, the basic control strategy for a VSG is introduced to analyze the influence of power angle on line power coupling. Then, based on the feedforward compensation strategy, an adaptive feedforward compensation power decoupling control strategy is introduced to compensate for the power coupling amount by adaptively modifying the feedforward compensation coefficient and eliminate the coupling between active and reactive power. A small-signal model based on the proposed adaptive feedforward compensation is established to analyze the impact of the adopted decoupling strategy on system stability. Finally, Matlab/Simulink simulation is used to verify that the decoupling control strategy not only effectively eliminates the coupling between power loops, but also significantly enhances the transient steady-state performance of the VSG output power.