This paper proposes an indicator for realizing power system voltage stability. This indicator is basically derived from Kirchhoff law. Hence, the indicator is easily calculated. Due to the requirement of power balance condition at anytime, this indicator can be realized during the transient process of electric power systems. The main advantage of the indicator is that it requires such a short time to calculate, so it can be used for online monitoring the state of voltage stability. Moreover, it is easy to find out the most vulnerable area and the collapse point of the given system by using this indicator. The effectiveness of the proposed indicator is verified by simulation results using the IEEE-14 bus system under various scenarios
