©　2002　IEEE.A　new　single-ended　fault　location　principle　for　EHV　transmission　lines　is　proposed　in　the　paper,　which　is　based　on　the　telegraph　equations,　breaking　through　the　traditional　single-ended　fault　location　principles.　By　analyzing　the　solution　of　telegraph　equations,　the　calculated　voltage　profile　along　the　faulted　line　using　single-ended　data　is-false　behind　the　fault　point,　however　the　differential　function　of　the　fictitious　voltage　profile　to　distance　x　is　minimum　at　the　fault　point,　by　which　the　fault　principle　is　constructed.　The　EMTP　simulation　tests　show　that　the　algorithm　has　the　quality　of　more　accurate　and　fault　resistance,　fault　type,　and　fault　inception　angle　do　not　affect　the　located　results.