The invention discloses a primary frequency modulation dynamic regulation method and device based on AGC reverse regulation. When the frequency fluctuation of a power grid exceeds a limit, according to whether a unit is in an AGC dynamic regulation process or not, whether AGC and primary frequency modulation reverse regulation exists or not is judged, and if a reverse regulation condition exists,difference compensation regulation calculation is carried out on a primary frequency modulation compensation amount according to a time point of an AGC and primary frequency modulation action; a loadincrement of required difference compensation regulation is superposed to the original primary frequency modulation compensation amount; and dynamic compensation regulation of a target value of a loadof the unit is carried out. The range of the primary frequency modulation action can be effectively ensured to meet the requirement of power grid frequency compensation; the accuracy of primary frequency modulation response of dispatching in the thermal power unit is improved; the action percent of pass is improved; and the frequency fluctuation of a power grid system is reduced.