It is necessary to quantitatively evaluate the frequency regulation capability of wind power, so as to make the best of the frequency regulation potential and avoid excessive frequency regulation. Therefore, a method considering operating point offset of wind turbine is proposed to evaluate frequency regulation capability. Firstly, a frequency regulation model of wind turbine based on integrated virtual inertia control is constructed. According to the model, it is pointed out that the wind turbine will shift the operating point during frequency regulation. Secondly, considering the mechanical power loss caused by the wind turbine’s operating point offset, the numerical relationship between the available power and the rotor speed is derived, so as to quantify the frequency regulation ability of the wind turbine. On this basis, the variation of the available power of the wind turbine under different operating conditions is analyzed, and the influence mechanism of wind speed and other factors on it is revealed. Finally, the effectiveness is verified by simulation example.