Power transformers are critical in power systems and the stable operation of power transformers is a vital guarantee of system stability. However, with the development of capacity and voltage level, the external short-circuit fault threats the stable and secure operation of power transformers more seriously than ever before. Transformer windings experience complicated dynamic deformation transient process during external short-circuit faults, and many issues still remain unknown in the field of winding deformation simulation and analysis. In view of this, this paper deals with the simulation and analysis of the transformer winding deformation characteristics. At first, the mathematical model of winding deformation concerning magnetic field and solid mechanic field is presented and demonstrated. Furthermore, a 3D geometric simulation model is established based on the actual size parameters of a 500 kV single-phase two-winding transformer. Based on this, the muti-physic-field coupling technique based on the finite-element method (FEM) has been employed to calculate the dynamic deformation characteristics of transformer winding structures during the transient process. The simulation result indicate that ideal intact windings can withstand the most severe impact from external short-circuits without plastic deformation. Even so, relatively heavy radial deformation will appear in the middle position near return yokes. Consequently, the winding structure in the middle-height position near the ferromagnetic circuit should be checked and strengthened to prevent windings from plastic deformation and radial instability.