Based on a 10kV distribution system, a new voltage sag source location and recognition method is brought forward. With limited data, determine the voltage sag location according to the flow of the energy in the system. Make an analysis on characteristics of several common voltage sag source from the balanced of three-phase voltage, sag depth, changes of active power and Total Harmonic Distortion of voltage. According to the characteristics of the source and simulation, the criterion has been established. Then achieve the location and recognition of the voltage sag source caused by power system short-circuit faults, start up of induction motors and energization of power transformers.