The invention provides transformer electromagnetic-conversion methods and devices based on current decomposition and winding equivalence. Firstly, current equations and electromotive force equations of a transformer are constructed, then an equivalent circuit of the transformer is determined according to the current equations and the electromotive force equations of the transformer, and finally, conversion of the transformer from a magnetic circuit model to the equivalent circuit is realized. According to the technical solution provided by the invention, the advantages of both a UMEC method and a duality principle method are combined, the equivalent circuit of the single-phase two-winding transformer/three-phase three-column transformer corresponding to each magnetic circuit branch in themagnetic circuit model can be obtained, a specific topology structure of the equivalent circuit can be intuitively expressed, and the method has very high observability. In the technical solution provided by the invention, calculation of magnetic permeance and magnetic permeability related to the single-phase two-winding transformer and the like, especially magnetic permeance and magnetic permeability related to the three-phase three-column transformer, is relatively simple, relatively small in calculation amounts and easy to operate.