Extended Debye equivalent Circuit of transformer is an important way to analyze insulation aging of transformer,Aiming at the problem that the number of polarization branches and the parameters of transformer equivalent circuit are difficult to solve,this paper proposes the depolarization current time domain micro-decomposition spectrum method according to the theory of dielectric polarization response,and decomposes the components of each sub-line in the depolarization current curve to determine the number of polarization branches and the identify equivalent circuit parameters according to the parameters of the sub-spectral lines. It provides a reliable and simple method for the construction of the equivalent circuit which accurately reflects the oil-paper insulation condition of transformer.The paper finally verifies the effectiveness of the proposed method by comparing with other identification methods, and further provides an important basis for the accurate evaluation of transformer insulation.