The invention belongs to the field of power systems and in particular relates to a method for modulating the active power output of a wind turbine by using an additional damping controller and improving the low-frequency oscillation damping characteristic of a large-scale wind power station grid-connected system. In the invention, according to a basic principle of controlling the optimum rotary speed of a double-fed wind turbine, a low-frequency oscillation characteristic signal of an alternating current power grid after interference is introduced to design the additional damping controller, the additional damping controller outputs a modulation component for controlling the rotary speed of a fan, and adjustment of the active power output of the wind turbine is realized by controlling the rotary speed of the fan, so an effect of restraining system oscillation is achieved. By applying the method to a large-scale grid-connected wind power station, the low-frequency oscillation damping characteristic of the system after interference can be improved; the system oscillation is quickly restrained; and capability of receiving large-capacity new energy source power of a power grid is improved.