This book presents the application of FACTS device in power system. The FACTS device is placed at mid-point location in AC transmission line system and simulated to control the active and reactive power flow using MATLAB. The FACTS device consider as UPFC. Simulation is performed in 5 bus system for results. Further, the FACTS device is checked for its performance. With the help of use of FACTS device in AC transmission line system,it is easily to improve and maintain other parameters in power system.