The invention provides a method for a variable-speed wind turbine generator to participate in frequency modulation of a power system. The method comprises the following steps: (1) initializing a powermargin, a pitch angle, an active instruction, a rotating speed and the like; (2) judging whether the rotating speed is greater than a rated rotating speed; (3) if the rotating speed is greater than or equal to the rated rotating speed, determining the electromagnetic torque, and if the rotating speed is less than the rated rotating speed, performing overspeed control by using the FIG. 1 deloadingcurve until the rotating speed is greater than or equal to the rated rotating speed; (4) determining the electromagnetic torque, and determining the pitch angle corresponding to the optimal electromagnetic torque by applying the relation curve of the pitch angle and the torque; and (5) judging whether the system frequency is normal, if yes, returning to the step (2) and if not, releasing the rotor kinetic energy to respond to the system frequency change.