By　analyzing　the　characteristic　of　WPT,　a　method　of　gaining　the　energy　eigenvector　of　transformer　tank　vibration　based　on　the　wavelet　packet　is　brought　forward　and　the　eigenvector　can　be　used　for　monitoring　the　transformer　core　condition.　The　vibration　signals　of　transformer　core　at　no-load　condition　are　tested.　Compared　to　the　normal　condition,　when　the　core　has　been　at　defect　there　are　exiguous　changes　at　the　time-domain,　thus　an　affirmatory　criterion　can　not　been　gained　to　assess　the　degree　of　the　transformer＇　defect.　The　vibration　signals　are　analyzed　using　WPT-arithmetic　and　the　energy　eigenvectors　are　gained.　From　the　result　of　experiment,　we　can　see　this　method　is　very　useful　to　estimate　the　condition　of　the　transformer　core.