A coordinated multi-control area automatic generation control (AGC) model is proposed to solve the problem of power sent. Combined with the model, the role of the relationship between power flow and the behavior of AGC is analyzed and the corresponding control strategy and control algorithm are given. Control objective for the main control area is frequency and tie-line bias control. Control objective for the sub-control area is close to the permissive bounds of stable control requirements. In order to achieve a coordinated control between sub-control area and the main control area, sub-control area can also be involved in the control of the main control area. Actual application of the proposed method to the AGC in Yunnan Provincial Power Dispatching and Control Center shows that this method can effectively keep the sub-control area power flow of tie line within the permissive bounds and ensure the secure and stable operation of power system.