In　order　to　construct　a　reliable　oil-paper　insulation　transformer　equivalent　circuit　so　as　to　further　study　the　inner　link　between　damping　condition　of　oil-paper　insulation　and　dielectric　relaxation　response,　we　put　forward　a　method　based　on　depolarizing　current　differential　spectrum　to　identify　the　parameters　of　extended　Debye　model　equivalent　circuit　model.　Firstly,　we　differentiate　the　depolarizing　current　to　reveal　its　interior　relaxation　response　information.　Research　shows　that　the　number　of　equivalent　circuit　relax　branches　is　just　the　number　of　peak　points　of　the　depolarizing　current　micro-spectrum.　Then,　we　theoretically　analyze　the　relationship　between　the　first　micro-spectrum　functional　expression　of　depolarizing　current　and　equivalent　circuit　parameters,　and　decompose　the　first　micro-spectrum　to　obtain　the　corresponding　sub-line　parameters.　The　study　reveals　that　the　relax　branch　parameters　of　equivalent　circuit　model　are　identified　accurately　from　the　sub-line　parameter　of　depolarization　current　differential　spectrum.　Finally,　examples　are　given　to　verify　that　the　method　is　efficacious.　The　analysis　results　show　that　the　proposed　method　provides　a　correct　mathematical　diagnostic　model　for　evaluating　the　relaxation　response　characteristics　of　the　oil-paper　insulation　transformer.　©　2016,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.