Power　transformer　tank　bulging,　rupture,　even　explosion　occurs　from　time　to　time　when　suffering　internal　short-circuit　faults.　The　resulting　disasters　such　as　oil　spray　and　fire　greatly　jeopardize　the　safety　of　nearby　staffs,　apparatus　and　public　environment.　In　order　to　reveal　the　mechanism　of　abrupt　oil　pressure　increase　and　successive　tank　deformation　and　rupture　inside　the　transformer,　this　work　describes　this　complex　process　with　two　separate　stages,　i.e.　fault　pressure　and　tank　stress.　The　model　and　corresponding　solution　of　each　stage　is　provided　respectively.　Firstly,　the　transformer　fault　pressure　model,　tank　transient　mechanical　model　and　pressure-mechanical　field　coupling　model　are　introduced.　Based　on　the　law　of　energy　conservation,　the　relationship　among　the　fault　energy,　oil　pressure　and　stress　is　interpreted.　Secondly,　a　3D　finite　element　model　is　built　for　a　360　MV·A/220　kV　power　transformer.　In　addition,　the　stress-strain　relationship　of　the　tank　wall　is　described　by　employing　a　multi-linear　isotropic　hardening　model.　Thirdly,　the　distribution　and　variation　of　the　internal　fault　pressure　and　stress　in　the　transformer　tank　wall　are　simulated　and　analyzed　for　a　variety　of　fault　locations　and　severities.　The　simulation　results　show　that　some　positive　correlations　exist　among　the　fault　energy,　oil　pressure　amplitude　and　tank　stress.　It　is　also　found　that　countermeasures,　such　as　rapid　fault　clearance　and　reinforcements　for　the　stress　concentration　area,　are　helpful　to　improve　tank＇s　capability　of　overpressure　endurance　and　to　reduce　the　risk　of　oil　spray,　fire,　tank　explosion　and　other　secondary　disasters.　©　2016,　The　editorial　office　of　Transaction　of　China　Electrotechnical　Society.　All　right　reserved.