This paper introduced a method to maintain system voltage within the optimal range and prevent voltage instability phenomena before they occur employing multiple agents. The proposed system divided the traditional method to control voltage and reactive power into two sub problems, “voltage control” to adjust the secondary bus voltage of substations, and “reactive power control” to adjust the primary bus voltage. In the proposed system, the two kind of agents employed performed their respective roles well. The voltage control adjusts the secondary voltage in own substation and the primary voltage of same voltage class. In addition, in order to equalize the primary bus voltage among different substations, each substation adjusts the reactive power. In order to verify the performance of the proposed method, it has been applied to the model network system. The results confirm that our proposed method is able to control violent fluctuations in load.