The invention relates to a frequency modulation method and device for a large-scale wind generating set. The frequency modulation method comprises the following steps: under the condition of reservingset reserve capacity, determining a corresponding relation between the power and the pitch angle of the wind generating set; in the generating operational process of the wind generating set, judgingwhether the real-time generated power of the wind generating set is greater than variable pitch energy storage initial power or not; if the real-time generated power of the wind generating set is greater than variable pitch energy storage initial power, controlling the wind generating set according to the determined corresponding relation between the power and the pitch angle of the wind generating set; detecting the frequency of a power grid in real time, and carrying out the frequency modulation control of the power grid by adopting the reserved set reserve capacity. According to the frequency modulation method, under the premise of without adding set hardware equipment, the capacity reserve of the set is realized in a variable pitch energy storage manner by optimizing the main control strategy of a draught fan, reserve power is provided for carrying out active frequency modulation on the draught fan, the supporting capacity of the wind generating set for the power grid is strengthened, and the method is beneficial for popularizing large-area network operation of the wind generating set.