The invention provides a wind farm frequency modulation method and device under a power-limited condition. Each wind turbine group in the wind farm is divided into A class, B class, C class, D class and E class wind turbine groups according to an actual operating condition, the A class, B class, C class, D class and E class wind turbine groups are orderly called according to a preset distributionstrategy, the active frequency modulation of a wind farm is achieved, the use of abandoned wind power is maximized, the frequency modulation mode of wind turbines under a power-limited condition and the active power adjustment amount of each wind turbine in the wind farm are fully considered, the reserved capacity reserved by each wind turbine is reasonably used, the distribution of active power adjustment is optimized, so a condition that the wind farm accurately responds to a frequency variation of a power system can be ensured, and the accuracy and economy of the wind farm frequency modulation are considered.