A growth of penetrations of photovoltaic and wind power generation make it difficult to maintain frequency stability because of unexpected intermittent power production depending on the weather. To keep supply-demand balance, increase of reserve capacity for frequency control is essential. However, if large fluctuation of RES outputs is absorbed by large amount of reserves, large fluctuated power propagates in transmission lines. The increase of power flow fluctuation cause deterioration of power system stability or damage of transmission line. This paper proposes a novel method for suppressing power flow fluctuation by arranging Automatic Generation Control (AGC) order dispatching. The proposed method optimize the dispatching ratio by considering impact of AGC order implementation on the power flow of target lines by using power flow sensitivity coefficient. The validity of the proposed method is verified by simulation study based on 10-machine power system model and the result shows that appropriate picking up of target line reduce power flow fluctuation effectively.