Cables　are　very　important　in　urban　power　system　due　to　the　small　occupied　area　and　excellent　electrical　properties.　However,　the　breakage　defect　caused　by　manufacturing　errors　and　improper　installation　can　lead　to　great　loss　to　the　power　system.　Thus,　the　localization　and　assessment　of　breakage　defect　is　necessary.　In　this　paper,　a　non-destructive　method　based　on　time–frequency　domain　reflectometry　is　utilized,　and　the　position　and　degree　of　breakage　defect　can　be　obtained　by　the　peaks　of　the　localization　curve.　Besides,　pseudo　Wigner–Ville　distribution　is　proposed　to　avoid　the　cross-term　interference　problem　in　time–frequency　domain　reflectometry.　In　experiments,　breakage　defects　of　different　degrees　were　caused　to　the　same　position　of　the　target　cable.　The　defects　are　localized　accurately　with　errors　less　than　1%　of　the　entire　cable　length,　and　as　the　degree　of　damage　increases,　the　peak　value　of　the　assessment　curve　at　the　defect　becomes　larger　accordingly.　©　2022　The　Author(s)