Trucks　have　the　problems　of　frequent　braking　and　long-term　braking　during　long-slope　transportation.　As　the　temperature　of　the　traditional　eddy　current　retarder　is　as　high　as　500　°C　during　braking,　the　braking　torque　of　the　retarder　is　seriously　degraded.　According　to　the　principle　of　eddy　current　braking　and　current　thermal　effect,　this　paper　proposes　an　eddy　current　retarder　in　which　both　the　stator　and　the　excitation　coil　are　water-cooled.　The　multi-field　coupling　and　bidirectional　data　transmission　model　of　stator　temperature　field,　coil　temperature　field　and　transient　electromagnetic　field　are　established.　The　relationship　between　the　braking　torque　and　the　working　time　is　analyzed　under　continuous　braking　conditions,　considering　the　stator　temperature　and　the　temperature　of　the　excitation　coil.　It　provides　theoretical　support　for　the　optimal　design　of　the　retarder.　A　test　prototype　of　a　water-cooled　eddy　current　retarder　was　manufactured,　and　a　bench　drag　test　was　carried　out.　The　calculation　results　show　that　the　numerical　simulation　method　of　coupling　between　the　stator　temperature　field,　the　coil　temperature　field　and　the　transient　electromagnetic　field　is　adopted,　and　the　simulation　values　of　the　braking　torque　is　in　good　agreement　with　the　experimental　values.　©　2013　IEEE.