In order to improve the damping effect of the wind farm on the power system，this paper proposes a novel active power control strategy and analyzes the impact of communication time-delay on the control strategy.Firstly，the mechanism of the wind farm restraining oscillation of the power system is studied and an analytical condition for enabling the dynamic behaviors of the wind farm to be improved is derived.According to the condition，the additional control strategy is designed for the purpose of producing positive damping to the power system.The frequency increment is collected from the common bus of the wind farm as the input signal of the controller.Meanwhile，the output signals from the controller are individually transmitted to the active control loops of each wind turbogenerator.Secondly，considering the impact of commutation time-delay on the system performance，two propositions，as the constraining conditions for the design of the active power controller，are presented and proved，the proposition of solving the critical time-delay of the wind farm in supplying zero-damping and the critical time-delay resulting in Hopf bifurcation with the calculating system due to the wind farm supply to the power system with negative damping.Finally，as shown by simulation results，the additional active power control can markedly enhance the damping of the power system.Furthermore，it is found after introducing the time-delay factor that，with the time-delay increase，system damping varies as a result.The correctness of the analytical condition and the two propositions are verified by the root locus analysis and frequency domain analysis.