UNIFIED POWER FLOW CONTROLLER (UPFC), AS A INDICATIVE OF THE THIRD GENERATION OF FACTS DEVICES, IS BY FAR THE MOST ENCYCLOPAEDIC FACTS DEVICE, IN POWER SYSTEM STEADY-STATE IT CAN ACCOMPLISHMENT POWER FLOW REGULATION, REASONABLY CONTROLLING LINE ACTIVE POWER AND REACTIVE POWER, IMPROVING THE TRANSMISSION CAPACITY OF POWER SYSTEM, AND IN POWER SYSTEM TRANSIENT STATE IT CAN REALIZE FAST-ACTING REACTIVE POWER RESTITUTION, DYNAMICALLY SUPPORTING THE VOLTAGE AT THE ACCESS POINT AND IMPROVING SYSTEM VOLTAGE STABILITY, MOREOVER, IT CAN IMPROVE THE DAMPING OF THE SYSTEM AND POWER ANGLE STABILITY. THE PRESENT PAPER SHOWS HOW THE UPFC INCREASES THE TRANSMISSION CAPACITY AND REDUCE THE POWER AGGLOMERATION IN THE TRANSMISSION LINE. TO STUDY THE PERFORMANCE OF THE USE OF THE UPFC ON AN EXISTING TRANSMISSION LINE, THE SIMULATION CARRIED OUT USING MATLAB-SIMULINK ENVIRONMENT.