Base on the power flow formulations, a new power flow model that allows for power exchanges among subareas of network and automation generation control in each subarea, is established. The proposed power flow model is rendering by unified newton iteration formulation. Parameters representing the level or allocation of the unbalancing power are introduced to indicate the performance of the generators that participate in the automation generation control. The power exchange formulations for subareas are derived from the power flow equations of the interconnected branches. The Newton iteration method is used to solve the equations that consist of node power injection equations and interconnected power equations. Because of the consideration of the power balance in each subarea and the order of power exchange, the presented method is applicable for power flow problems of interconnected power networks, and is in particular applicable for the system analysis and calculation that based on the uniform iteration formulation. Case studies of IEEE 5 bus test system and IEEE RTS96 system illustrate the efficiency and the convergence of the proposed method.