The invention relates to a primary frequency modulation method based on machine inlet pressure compensation, comprising the following steps of: carrying out pressure correction on action amount of a primary frequency load compensation curve F(x) by adopting the following formula: delta MW=delta MW1*Pt/Pe, wherein the delta MW is the power action amount after pressure correction, the delta MW1 is the power action amount of the original design, Pe is rated machine inlet pressure, and Pt is machine inlet pressure, therefore, the pressure compensation of primary frequency modulation can be realized; in addition, adding a high limit and a low limit on the action amount of the primary frequency load compensation curve F(x) after pressure compensation, and locking the machine inlet pressure in the primary frequency modulation action process. By adopting the technical characteristics, the primary frequency modulation action can be carried out on a machine set which participates in the primaryfrequency modulation of a power grid according to the load variation required by the power grid, therefore, the power supply quality of the power grid can be improved, and the primary frequency modulation requirements of the power grid to the machine set can be satisfied.