Lightning　impulse　has　the　biggest　influence　on　the　insulation　structure　of　power　transformer,　which　may　lead　to　transformer　breakdown.　When　the　transformer　is　subjected　to　lightning　impulse,　the　complex　electromagnetic　process　will　be　produce　on　the　winding.　The　overvoltage　distribution　along　the　winding　is　a　very　important　issue　for　the　designers　of　insulation　structure.　In　this　paper,　a　35kV　cast　resin　dry-type　transformer　is　taken　as　an　example　to　establish　the　FEM　simulation　model.　The　inductance　and　capacitance　distribution　parameters　of　the　high　voltage　winding　are　analyzed　and　calculated.　Then,　according　to　the　actual　structure　of　the　transformer,　each　section　of　coil　is　divided　into　one　unit　for　the　equivalent　circuit　of　transformer.　The　transient　overvoltage　distribution　of　each　section　under　the　action　of　lightning　voltage　is　analyzed　by　using　the　Simulink　simulation　toolbox　of　MATLAB.　For　more　detailed　research,　each　section　is　remodeled　as　a　sub　model　that　each　turn　conductor　is　divided　into　a　unit.　The　ground　voltage　of　each　turn　and　turn　to　turn　voltage　under　lightning　impulse　are　calculated.　The　results　show　that　due　to　the　existence　of　the　distributed　inductance　and　capacitance,　there　is　a　hysteresis　and　oscillation　in　the　potential　of　each　section.　The　maximum　potential　exceeds　the　peak　of　the　lightning　impulse　voltage,　and　appears　at　Section　3,　4,　5,　which　near　the　low　voltage　windings.　At　about　10μs,　potential　of　Section　3,　4,　5　rises　to　the　maximum,　and　electric　field　is　concentrated　in　the　air　channel　between　the　high　and　low　windings,　which　is　about　3.5　kV/mm.　The　front　and　the　end　sections　have　maximum　voltage　between　sections　and　maximum　electric　field　between　turns.　©　2018　IEEE.