In this paper, the influence of transformer winding deformation on the equivalent electrical parameters is studied, and the proximity effect and skin effect caused by AC current in the wire are simulated. It is verified that the current distribution will be affected by the proximity effect and skin effect. This effect will lead to the change of the AC resistance of split conductor. An equivalent area method for the quantitative calculation of the high frequency resistance of windings is presented. It contributes to the analysis and diagnosis of transformer winding faults, especially the diagnosis of transformer winding deformation.