The high proportion of wind power access to power systems leads to a reduction of the equivalent inertia of the system. This increases the possibility of frequency instability caused by the power grid. In order to ensure the safe and stable operation of the frequency during the day, and at the same time avoid the unreasonable step of removing wind power in a large area, a method of limiting wind power output based on frequency safety constraints and a critical inertia calculation is proposed. By introducing a frequency nadir and maximum rate of change of frequency constraint index, and considering the changes in the operation mode within the day, the critical inertia of the grid and the corresponding maximum wind power grid-connected capacity are calculated in time periods. A time period less than the critical inertia is determined based on the actual inertia of the grid, to determine the amount of wind power removal based on the maximum wind power grid-connected capacity. This is to eliminate hidden frequency safety hazards at various times of the day. Finally, a calculation example proves that the method proposed in this paper can accurately screen the time period of frequency safety risk in the grid day, and the calculated amount of wind power cut in time can effectively eliminate the hidden frequency safety hazard. This work is supported by the National Natural Science Foundation of China (No. 51907104).