In recent years, the number of small size wind farms used as DG sources located within the distribution system are rapidly increasing. In this paper, wind farm made up with doubly fed induction generators (DFIG) is proposed as the continuous reactive power source to support system voltage control due to the reactive power control capability of DFIG. The particle swarm optimization (PSO) is utilized to find wind farm optimal reactive power output for distribution system losses reduction and voltage profiles improvement. Finally, the three feeder distribution system is used as a test case to evaluate the algorithm.