With the rapid development of modern power electronic devices and the rapid development of the new type of power load,the problem of power quality is paid more and more attention.In order to study the voltage sags better impact on the power system,firstly,according to the source voltage sag event classification,including the main source of short-circuit fault,large motor starting and lightning,then the voltage sags caused by short circuit fault identification,can make the voltage sag monitoring system according to the waveform recognition a fault type.Finally,through the case analysis of the data waveform of the voltage sag monitoring system in Jiangsu power grid,the paper classifies the four kinds of typical short circuit faults,and verifies the feasibility of the algorithm.