There are two key points in the modeling calculation method of transformer. One is the representation of magnetization curve, and the other one is the equivalent conversion model from magnetic circuit to electric circuit. A new conversion model is proposed to solve the second key point. It equalizes the iron core, iron yoke and magnetic flux leakage to winding coils which have the primary number of turns. And then the method of disassembly current is used to represent the relationship of each coil current and the continuity of magnetic flux is used to represent relationship of electromotive force, which obtain the electric circuit model equivalent to magnetic circuit. The circuit model is the same as that obtained by duality theory method. And the electric circuit model can obtain the same dynamic self-inductance and mutual inductance which are obtained by the unified magnetic circuit UMEC method. It verifies the validity of the proposed new method and proves the oneness of proposed method, duality method and unified magnetic circuit method. Finally, the flow chart of electromagnetic simulation considering transformer saturation is given.