The invention discloses an inter-region active power automatic support method of an interconnected network. With regard to a regional power grid having two-stage dispatching real-time data interactionof a branch dispatching center and a provincial control region, active power support total amount is calculated according to power grid frequency deviation when the power grid frequency deviation ofthe regional power grid exceeds a set support limit value, the active power support total amount is allocated to the provincial control region participating in support, the purpose of changing ACE ofthe provincial control region participating in support is achieved by changing an exchange plane of the provincial control region participating in support, and active power automatic support between interconnected network regions is achieved; and with regard to a regional power grid which does not have the two-stage dispatching real-time data interaction of the branch dispatching center and the provincial control region, different ACE calculation methods of the provincial control region are employed according to different zones where the power grid frequency deviation is located, and active power automatic support between the interconnected network regions is performed according to the ACE of the provincial control region. By the active power automatic support method, rapid recovery of thepower grid frequency can be achieved.