Based　on　the　recovery　voltage　test　datum,　the　rough　set　theory　is　used　to　evaluate　the　insulation　status　of　the　transformer　and　a　transformer　insulation　status　evaluation　system　is　established.　Firstly,　the　characteristics　of　the　recovered　voltage　method　and　the　extended　Debye　equivalent　relaxation　circuit　are　selected　as　the　evaluation　features.　Then,　the　fuzzy　C-means　clustering　algorithm　is　used　to　divide　the　quantities　of　evaluation　features　into　fuzzy　indicators　and　generate　the　insulation　status　decision　table.　The　discrepancy　matrix　performs　attribute　reduction　on　the　insulation　status　decision　table.　Finally,　the　blind　reduction　value　reduction　algorithm　is　used　to　reduce　the　attribute　value　of　the　reduced　decision　table,　and　a　complete　reduction　decision　table　is　obtained.　On　this　basis,　the　transformer　insulation　status　evaluation　rule　table　is　established.　The　example　analysis　proves　that　the　proposed　evaluation　method　can　effectively　evaluate　the　internal　insulation　status　of　the　transformer.　©　2019,　Power　System　Protection　and　Control　Press.　All　right　reserved.