The invention provides a wind farm active power control method. The active power output of a wind farm is dynamically adjusted online by means of variable pitch and startup-shutdown according to a scheduling order of a power grid and under the premise of ensuring the service life of fans, considering the working conditions of fans and reducing fan failure. According to the control method put forward by the invention, a set value can be tracked quickly and accurately, and the generation power can be limited below a limit value by overshooting. When a unit is shut down due to failure, a target generation power can be allocated according to the failure state of the unit to make the real-time generation power quickly restore to a target value. Through centralized control on wind turbine generator units in a wind farm by use of the power control method, the quality of electric energy output by the wind farm is improved, the stability of the output power of the wind farm is ensured, and the adverse impact of the randomness and volatility of wind power generation on the power grid is reduced.