Return　voltage　measurement　is　an　effective　non-destructive　testing　method　for　diagnosis　of　transformer　insulation　state.　Establishing　transformer　dielectric　response　equivalent　circuit　model　is　an　effective　way　to　analyze　the　relationship　between　insulation　aging　and　characteristic　quantity.　Therefore,　on　the　basis　of　establishing　equivalent　circuit　mathematical　model,　equivalent　circuit　parameters　identification　was　transformed　into　the　mathematical　optimization,　then　the　improved　ant　colony　algorithm　was　adopted　to　identify　model　parameters.　Four　test　functions　proved　that　using　both　global　optimal　solution　and　each　iteration　optimal　solution　in　global　pheromone　updating　could　improve　convergence　speed,　expand　search　scope,　and　using　the　dynamic　local　pheromone　updating　could　also　strengthen　the　ability　of　jumping　out　of　local　optimal　value.　The　contrast　of　polarization　spectra　between　model　calculation　and　practical　measurement　shows　that　the　solved　equivalent　model　can　accurately　reflect　the　medium　response　characteristics　of　oil-paper　transformer　insulation.