When　vibration　signal　analysis　method　is　used　to　monitor　the　transformer,　the　core　vibration　signal　is　often　obtained　as　the　transformer　runs　under　no-load　condition.　In　this　paper,　a　method　extracting　core　vibration　signal　without　operating　transformer　under　no-load　condition　was　introduced.　The　transformer　vibration　accelerative　signals　at　different　on-load　current　and　no-load　condition　were　measured.　From　the　fitted　curve　of　on-load　current　versus　fundamental　frequency　component　of　vibration　accelerated　signal,　the　value　of　fundamental　frequency　component　was　obtained　when　the　on-load　current　was　zero,　which　was　almost　equivalent　to　the　fundamental　frequency　component　of　vibration　accelerative　signal　measured　under　no-load　condition,　thus　the　fundamental　frequency　component　of　core　vibration　can　be　obtained　by　using　on-load　current　method.　The　core　with　fault　was　finally　monitored　by　using　the　on-load　current　method　compared　with　wavelet　package　transform　method.　From　the　result　of　experiment,　it　can　be　seen　this　method　is　very　useful　to　estimate　the　condition　of　the　transformer　core.　©　(2013)　Trans　Tech　Publications,　Switzerland.