This paper proposes the FACTS site selection method using subtransmission system reduction. A general method which uses the sensitivity of the variation in voltage and reactive power has been used to determine the location of shunt type FACTS device, but there is a difficulty to finding a proper location due to the overestimation of the effect of sub-transmission systems. Therefore, there is a need to reduce sub-transmission system for finding an effective location of shunt type FACTS devices such as SVC(Static Var Compensator), STATCOM(Static Synchronous Compesator), and so on.