To　further　explore　the　inner　link　between　oil　paper　insulation　aging　and　dielectric　relaxation　response,　the　inner　relaxation　characteristics　of　depolarization　current(DC)　are　investigated.　Two　new　characteristic　quantities　including　relaxation　spectrum　and　its　energy　are　introduced.　The　second　order　differentiation　method　is　applied　to　determine　the　number　of　depolarization　current　relaxation　spectrums,　and　aging　condition　of　oil-paper　insulation＇s　relationships　with　both　the　number　of　relaxation　spectrums　and　its　energy　are　discussed.　A　method　to　distinguish　aging　condition　of　oil-paper　insulation　is　derived.　Results　show　that,　as　the　dielectric　aging　is　deepening,　the　number　of　relaxation　spectrums　is　growing,　and　the　relaxation　spectrum　energy　is　sensitive　to　aging　condition　and　increases　with　the　lower　insulation　level.　The　number　of　relaxation　spectrums　and　its　energy　can　be　accepted　as　the　criterion　of　insulation　diagnosis.　An　effective　means　is　realized　to　assess　the　oil-paper　insulation　aging　status,　which　provides　a　certain　reference　value.　©,　2015,　Science　Press.　All　right　reserved.