Voltage　sag　is　one　of　the　major　power　quality　problems　that　maybe　result　from　networks　fault　and　sudden　increase　of　the　load.　It　will　result　in　abnormal　operation　or　shutting　down　of　device.　Sag　location　is　an　important　topic　because　power-quality　trouble-shooting,　diagnosis,　mitigation　policy　could　be　constituted　and　mitigation　measurement　be　carried　out　only　after　locating　the　voltage　sag　source　accurately.　A　method　based　on　the　impedance　measurement　in　dq0　coordinate　system　is　proposed　in　this　paper.　Firstly,　the　three-phase　voltage　and　current　measured　at　the　monitoring　point　are　transformed　by　the　orthogonal　Park＇s　transformation.　And　then　the　certain　character　of　obtained　three-phase　instantaneous　impedance　measurement　is　used　to　locate　the　sources　of　the　voltage　sags.　Constant　impedance　load　and　induction-motor　load　are　used　in　digital　simulation　respectively.　The　simulation　results　show　that　the　method　can　locate　the　disturbance　source　whether　symmetrical　or　asymmetrical　happens.　©2010　IEEE.