The problem of voltage safety and stability might occur when the wind power is connected to the power grid. In order to improve the voltage stability of the wind farm's grid connection point, this paper proposes a reactive configuration of the doublyfed wind farms on the basis of the calculation of load's safe domain. In addition, a collector line selection method is also proposed. Firstly, the P-Q characteristic curve of the wind turbine unit is derived, and the stable operation domain of the doublyfed wind turbine is obtained. Then, the P-Q characteristic curve and the boundary coordination problem of the safety end of collector line are analyzed to determine the collector line type, so as to fully utilize the nonfunctionality of the wind turbine. Finally, the reactive power allocation capacity of the wind farm is calculated through the security domain boundary of the grid connection point. The results of the example show that the proposed reactive power configuration method can ensure the grid voltage within the safe range.