The invention discloses a primary frequency modulation dynamic compensation adjustment system and method based on performance index evaluation. The system comprises a primary frequency modulation dynamic compensation adjustment calculation module, a frequency modulation dynamic compensation determination module, a frequency modulation dynamic compensation output module, a frequency modulation power constant-value compensation module, a comprehensive valve position increment compensation module and a comprehensive valve position command generation module. By performing dynamic compensation adjustment on a frequency modulation power setting and a comprehensive valve position increment, a moderate overshoot is used to ensure the rapid return of a grid frequency and ensure that a unit primaryfrequency performance index meets a standard requirement. The method calculates a dynamic compensation coefficient according to the amplitude of the primary frequency modulation operation at a relevant time point of the unit and the operation integral power amount in a corresponding time period, and adjusts the variation quantity of the primary frequency modulation of the unit in a targeted manner, thereby improving the accuracy of the thermal power generation unit to schedule the primary frequency modulation response, satisfying the demand of the grid for the unit primary frequency modulationoperation, ensuring its frequency modulation capability and reducing the frequency fluctuation of a grid system.