A method of distribution network voltage stability assessment with power circle index is presented. By means of calculating the index of voltage stability, security of power grid structures and reliability of power consumption, the composite indicator of the distribution network is introduced. The voltage stability is assessed in three steps: when wind farm is integrated into the network, the impulse current flowing through the power circle is calculated and voltage sag of load point is obtained to assess voltage stability; when it exits from the network, voltage stability is assessed by calculating voltage drop with the loss of voltage support; when it generates fluctuant power continually, the change of power flow in the network is considered and voltage stability assessment equation is reconstructed to determine voltage stability with active and reactive power of wind farm. Taking the IEEE123 as the sample, the effectiveness of the voltage stability assessment frame for distribution network with wind farms is proved.