Abstract: Voltage collapse could be caused by wind power operating at connecting node. Real time discrimination of voltage stability has significance for wind power connecting. In this paper, a voltage stability index which avoid using large number of information is structured based on equivalence of power system. The voltage stability of wind power connecting node can be online monitoring by the index with electrical information acquisition at the node. The index can exactly and timely distinguish the voltage collapse and voltage fluctuation in wind power connecting node which caused by sustained increasing of load and transient fault with simulation results.