The application relates to a multi-power dispatching mechanism AGC unified frequency modulation control method, device and system supporting a frequency modulation auxiliary service market, a computerdevice and a storage medium. The method comprises the steps of: obtaining the real-time frequency of a power grid, and determining the frequency adjustment requirement of the power grid according tothe real-time frequency of the power grid; obtaining a clearing result of the unified frequency modulation auxiliary service market and the operation information of each power dispatching mechanism AGC, and obtaining the regional control deviation of each power dispatching mechanism AGC participating in the unified frequency modulation control according to a frequency adjustment demand, the clearing result, and the frequency modulation data of each power dispatching mechanism AGC participating in the unified frequency modulation control; and sending the regional control deviation to the corresponding power dispatching mechanism AGC participating in the unified frequency modulation control in order that the corresponding power dispatching mechanism AGC participating in the unified frequencymodulation control obtains the newly added regional frequency modulation demand according to the regional control deviation, and allocates the newly added regional frequency modulation demand to a subordinate power generating unit according to the clearing result. The method can quickly dispatch the frequency modulation resources of the entire power grid.