A voltage control strategy is introduced for wind farms using the doubly fed induction generator（DFIG）. The strategy aims at controlling the voltage at the wind farms step-up transformer high voltage side. The overall configuration of voltage control and the principal are described， taking into account of the reactive power limits of wind turbines. The reactive power control， distribution and emergency voltage control under the system fault conditions are also studied. Both wind-speed variation and voltage-sag are simulated to compare the dynamic responses of the system with power factor control and traditional voltage control. Simulation results show that the voltage control strategy can maintain the wind farm voltage level without any additional feedback signal from high voltage side of the step-up transformer. The control strategy is proved to be economical and efficient.