Based on the theory of transformer magnetic field distribution and common transformer winding deformation, two-dimensional transformer ANSYS models when windings are normal or occur common types of axial deformation are established, and the relationship between transformer magnetic field distribution and windings deformation are intensively studied. According to the relationship between transformer magnetic field distribution and winding deformation, a method that realizing transformer windings deformation on-line monitoring by measuring magnetic field is proposed. Finally, the transformer windings deformation determination method and optimization of magnetic field sensor installation location are proposed.