The present invention discloses an active power distribution method of wind farm participating in automatic power generation control. The method comprises the following steps: setting a scheduling cycle, and initializing a wind farm active power output planned value demanded by the power grid; acquiring wind speed information of all wind power turbines, and taking the turbulent wind speed of the turbines in the previous cycle as the wind condition of the current scheduling cycle; calculating a statistical characteristic index according to the wind speed information of the turbines; bringing the statistical characteristic index into a decision tree to estimate the maximum available wind power, and setting the maximum available wind power as the output power upper limit of all wind power turbines; and determining the active output commands of all wind power turbines via a global optimal distribution method. According to the method, the maximum available wind power is taken as the constraint condition, the maximum available wind power is applied in the wind farm active power optimization distribution orienting towards automatic power generation control, the active output commands of all wind power turbines are reasonably distributed via a scheduling algorithm, so that the wind farm can smoothly respond the power generation commands scheduled and demanded by the power grid, and thus the smoothness of the wind farm participating in the automatic power generation control is improved.