The　optical　fiber　sensing　technology　has　the　advantages　of　long-distance　transmission　and　distributed　detection,　therefore　having　great　application　potential　in　the　field　of　cable　line　condition　monitoring.　In　this　paper,　a　phase-sensitive　optical　time-domain　reflectometry　(Φ-OTDR)　is　used　to　interrogate　partial　discharges　in　the　fault　diagnosis　of　power　cable　joints.　By　virtue　of　stochastic　features　of　the　Rayleigh　scattering　coherent　signal,　the　signal　variance　is　chosen　as　a　detection　quantity　of　the　weak　ultrasonic　signal.　In　the　partial　discharge　experiment,　five　fiber　loop　sensors　were　wrapped　around　some　ultrasonic　monitoring　points　on　the　cable　joint,　to　prove　the　distributed　locating　capability　of　the　Φ-OTDR　system.　The　signal　characteristics　of　the　electrical　measurement　method　and　fiber-optic　acoustic　measurement　method　for　local　discharge　were　compared,　and　the　positions　of　the　five　fiber　loop　sensors　were　calibrated　by　a　piezoelectric　sensor,　which　verified　the　features　of　the　Φ-OTDR　distributed　ultrasonic　fiber　sensors　in　partial　discharge　measurements.　©　2021,　Chinese　Lasers　Press.　All　right　reserved.