Being　aware　of　the　great　hazard　of　transformer　winding　deformation　and　insulation　damage　under　the　impact　of　huge　electromagnetic　forces　caused　by　short　circuit　faults,　this　paper　presented　an　analysis　method　based　on　explicit　dynamic　3-D　finite　element　method,　enabling　detailed　and　representative　investigations　of　the　mechanical　effects　of　external　short　circuit　faults　in　power　transformers.　Considering　the　displacements　and　deformations　of　windings　could　change　the　leakage　flux　distribution　and　further　influence　the　remaining　computation,　an　electromagnetic-mechanical　field　coupling　model　was　proposed.　To　accurately　calculate　the　windings　transient　deformation,　both　the　disks　and　spacers　were　considered　as　the　elastic-plastic　body.　Meanwhile,　the　high-voltage　and　low-voltage　windings　were　modeled　into　21　disks　and　18　spacers　are　evenly　arranged　between　the　adjacent　copper　disks.　For　illustrating　the　effectiveness　of　the　proposed　method,　a　real　full-scale　120　MVA/220　kV　oil-immersed　transformer　model　was　built　to　suffer　the　serious　three-phase　short　circuit　fault　as　the　case　study.　A　comparison　of　the　von-Mises　stress　distribution　in　healthy,　pre-strain　and　dislocation　windings　under　the　same　short　circuit　fault　confirmed　that　the　healthy　winding　can　withstand　the　impact　of　short　circuit　fault　without　any　unrecoverable　deformation;　insufficient　mechanical　strength,　pre-strain　and　local　dislocation　are　the　key　factors　to　winding　deformation,　rupture　even　collapse.　Additionally,　the　theoretical　model　and　simulation　method　can　be　used　as　a　substitute　for　costly　and　cumbersome　field　tests　in　faults　characteristics　analysis　of　transformer　windings.