The frequency stability of the wind power grid-connected system may be improved by the participation of wind turbines in frequency regulation. However, it is difficult for the existing droop control to coordinate the frequency response characteristics and the operating state of the wind turbine. An adaptive droop control strategy is proposed to make full use of the rotor kinetic energy to participate in frequency regulation and ensure the stable operation of the wind turbine considering the rate of change of frequency (ROCOF) and the rotor kinetic energy. Firstly, a coupling function between the droop coefficient and ROCOF is established by the piecewise function with the intervals of ROCOF according to the system frequency, which can be released to ensure more energy from wind turbines at the initial stage of the disturbance. In this condition, the frequency drop is slowed down due to the support of the wind turbine for frequency regulation. Besides, to avoid the over-deceleration of the wind turbine and secondary frequency drop, an influence factor on the rotor speed is introduced to adjust the droop coefficient according to the operating state of the wind turbine. Finally, a wind-thermal combined system simulation model is built on the MATLAB/Simulink platform to verify the effectiveness of the proposed control strategy. The simulation results show that the proposed strategy can effectively apply the rotor kinetic energy of the wind turbine to improve the frequency response characteristics of the system while ensuring the stability of the wind turbine speed.