Heavy-duty　vehicles　are　generally　equipped　with　a　non-contact　auxiliary　brake　system　to　ensure　safe　driving.　As　an　actuator　for　the　auxiliary　brake　system,　liquid-cooled　and　embedded　eddy　current　retarder　has　significant　advantages　in　braking　performance　compared　to　the　traditional　eddy　current　retarder.　The　braking　performance　is　better　with　the　smaller　gap　between　the　stator　and　rotor　of　the　retarder　proved　by　theoretical　analysis　and　the　finite　element　analysis.　The　small　gap　causes　conflict　between　the　stator　and　rotor　when　the　retarder　works　for　a　long　time.　The　paper　studies　thermal　influence　on　deformation　of　the　retarder　at　work　by　establishing　a　multi-field　coupled　finite　element　model.　And　the　results　of　the　numerical　simulation　show　that　the　maximum　radial　deformation　of　the　stator　is　0.54mm　when　the　braking　power　of　the　retarder　is　120kW.　The　numerical　simulation　results　are　basically　consistent　with　the　experimental　results,　which　proves　that　the　deformation　during　the　continuous　working　of　the　retarder　is　mainly　caused　by　thermal　strain.　This　research　provides　theoretical　basis　and　research　methods　for　gap　design　between　the　stator　and　the　rotor　and　material　selection　standards　for　high　power　electromagnetic　products.