Abstract: The losses calculation of wound core is significant in the optimization design stage of energy-saving transformer. Only the demagnetization effect inside the lamination is taken into account on present analysis, in spite of the divided-grade phenomenon on boundary magnetic flux density. As for large-scale wound core, the computed error from this discrepancy is pretty prominent. Thus the non-uniform distribution on boundary flux density should be discussed to serve for electromagnetic computation better. In this paper, the grain-oriented property of electrical steel and the permeability of insulation coating are taken into consideration, and the magnetic circuit network is created in strict conformity with the core layers. Then the analytical expression describing the boundary flux densities in different layers is obtained by skillful approximations. The non-uniform distribution of boundary flux density in cross section is clearly analyzed by finite-element analysis from a variety of layers, and it is taken as a standard to verify the effectiveness of divided-grade magnetic circuit model. Finally, the proposed model is provided into the core losses computation of actual energy-saving autotransformer, where the magnetic quantity included in classical formula is modified. Comparison results with the measured values of core losses reveal that the proposed method has a more precision to calculate the losses than the classical formula, where the average error is less than 5%.