Aiming　at　the　insufficiency　of　oil-paper　insulation　aging　state　evaluation　by　the　dielectric　response　theory,　a　method　for　diagnosing　the　oil-paper　insulation　of　transformer　is　proposed.　The　differential　spectral　curve　of　transformer　recovery　voltage　is　unfolded,　and　the　relationship　between　sub-curve　quantity　and　insulation　aging　state　as　well　as　the　relationship　between　relaxation　time　constant　ratio　Kτ　and　insulation　aging　state　are　analyzed　for　the　diagnosis　of　transformer　oil-paper　insulation　aging　state.　The　test　data　of　multiple　transformers　are　analyzed　and　conclusions　are　obtained:　the　time-domain　sub-curve　quantity　of　recovery　voltage　differential　spectral　curve　changes　according　to　the　oil-paper　insulation　state,　the　more　serious　the　oil-paper　insulation　aging　state　is,　the　bigger　the　sub-curve　quantity　is;　and　Kτ　can　be　used　to　diagnose　the　relative　aging　state　of　insulation　oil　to　insulation　paper.　©　2017,　Electric　Power　Automation　Equipment　Press.　All　right　reserved.