Large scaled wind farms are being connected to the power grid rapidly， which imposes a new challenge to the active power dispatch and control of power grids. A wind farm active power control strategy developed on the base of automatic generation control（AGC） function of the energy management system（EMS） is illustrated. The realization scheme of the control strategy is introduced， together with the related technical measures in communication mode of wind farms and the control logic of wind turbines. Actual test in wind farm proves that the proposed control strategy can achieve rapid and accurate control of active power.