Abstract: The voltage stability of power grid was briefly introduced，and the measurement method of voltage

stability of phasor measurement unit（PMU）based on state estimation was proposed. This method mainly aims at

the voltage change caused by the load rate change. The voltage stability under different load conditions and different voltage values was explained.Weighted least squares（WLS）method was used to estimate the voltage state of power system，and the measurement results were directly generated by PMU. In order to achieve the maximum utilization efficiency of PMU in power system，the greedy algorithm was used to solve the optimal placement problem（OPP）of PMU，and the optimal location of PMU was deduced by using voltage stability index and other voltage analysis tools. By using PMU in power system，the tedious iterative process of voltage state estimation in power system was optimized，and the optimal placement problem of PMU in power system was solved.

      Key words: optimal placement problem（OPP）；phasor measurement unit（PMU）；state estimation；voltage

stability indices；weighted least squares（WLS）method