Abstract: Variable speed constant frequency (VSCF) wind turbines are connected to the grid through power electronic equipment, leading to the decoupling of wind turbine’s rotor speed and system frequency. As a result, the wind turbines cannot actively respond to the changes of system frequency. To cope with the system frequency stability problem resulting from large-scale integration of wind power, a new active power control strategy for wind farms is proposed, which preferentially applies overspeed de-loading control to wind turbines operating in low wind speed zone. Accordingly, the kinetic energy stored in the rotating mass of wind turbines can be maximized. In the meantime, the reserve demand of the system required by the transmission system operator can be met by applying pitch angle control to wind turbines operating in high wind speed zone. Furthermore, a virtual inertial control strategy with variable parameters is proposed, and the droop coefficient is tuned to ensure the full release of the reserve power of the wind turbines during the system frequency regulation. A system simulation model is built in the DIgSILENT, and the simulation results show that the proposed strategy can reasonably allocate the reserve power of wind turbines and effectively use the reserve power to respond to the frequency change of the system, thus improving the frequency control capabilities of the wind turbines.