The invention provides a power frequency modulation control method and device based on a virtual synchronous machine. When the frequency of a power grid is normal, the torque of a wind turbine is reduced, a rotation speed of a motor speed is increased, and the generated excess energy is stored; when the frequency of the power grid changes, the torque given value is restored into a given value of an optimal power curve of the wind turbine, and the energy is released. The method and device improves the frequency modulation response speed, solves the problem of slow frequency modulation responsespeed due to slow variable pitch speed, can provide active coordination when the wind field frequency fluctuates, can realize the stability of the power grid frequency, and can enhance the anti-interference ability of the power grid; and the control effect can make the change of the wind field to the power grid frequency behave as the external characteristic of the synchronous machine.