This paper proposes the cooperative control method between reactive power compensation devices for securing the reactive reserve power of the FACTS in the power system. The Cooperative control consists of the two different methods, such as concurrent and sequence control. This proposed method is used different method according to the normal and abnormal state. The concurrent control is applied for maintaining the bus voltage in desired level when the load of power system has been remarkably increased or decreased. This control method is operated at once by calculating necessary active power capacity based on the voltage difference to each substation voltage and reference voltage in the power system. The sequence control has been used to secure momentary reactive power. The momentary reactive power is processed with the fast control characteristics. Therefore, this control has been managed for improving the voltage stability in the power system. Also, it has been demonstrated by the PSS/E and the Python programs.