The invention relates to the technical field of fault distinguishment in an electric power system, in particular to a method for distinguishing transient state instability of the electric power system in real time based on voltage track after disturbance. The method comprises five steps, namely, selecting a voltage observation node, identifying voltage drop after fault clearance, complexly integrating the voltage track, distinguishing the transient state instability of the electric power system and identifying the fact that local voltage is over-low. The method for distinguishing the transient state instability of the electric power system in real time based on the voltage track after disturbance, disclosed by the invention, aims to solve a problem of system transient state instability caused by large disturbance out of a two-defense-line control range based on a measurement configuration of the existing phasor measurement unit ( PMU ) and a wide area measurement system ( WAMS ) in a power grid, and has the advantages of simple algorithm, low calculated quantity, less dependence on data precision and high reliability.