Abstract: In recent years, with the increasing penetration of wind power in power system, the inertia of power system is reduced, and the frequency stability of power grid is facing great challenges. In view of the above problems, this paper proposes a nonlinear frequency control strategy for wind power grid-connected system based on rotor kinetic energy release. First, the correction coefficient of wind turbine power reference curve is selected as the control signal, and the affine nonlinear system is established according to the mathematical model of wind turbine participating in grid frequency regulation. Secondly, based on the optimal control principle of partial linearization, the system is transformed into a second-order Brunovsky standard form to obtain the nonlinear control law, which avoids the problem of approximate linearization. Finally, the rotor speed function and speed recovery function are introduced to avoid the excessive decline of the wind turbine speed and complete the recovery of the wind turbine speed, without switching the control link. MATLAB/SIMULINK is used to build a wind power system for simulation verification. The results show that the nonlinear strategy of rotor kinetic energy has better frequency modulation effect than other strategies under the condition of releasing less kinetic energy, and it also improves the frequency stability of the power grid.