Heavy-duty　vehicles　are　generally　equipped　with　non-contact　hydraulic　retarders　or　eddy　current　retarders　to　ensure　safe　driving　during　downhill　conditions.　The　torque　of　the　hydraulic　retarder　is　large　when　the　rotor　rotates　at　a　high　speed,　but　the　torque　is　small　when　the　rotor　rotates　at　a　low　speed.　As　another　commonly　used　retarder,　the　eddy　current　retarder　has　a　large　torque　at　a　low　speed　and　a　low　power　density　at　a　high　speed.　High　torque　at　full　speed　is　the　vehicles＇　requirement　for　the　auxiliary　brake　system,　with　no　retarders　can　achieve　this　goal　perfectly　alone.　Encouragingly,　the　braking　performances　of　these　two　kinds　of　retarders　are　complementary.　Based　on　the　above　properties,　the　eddy　current-hydraulic　hybrid　retarder　(EHR)　is　designed　applying　the　principle　of　eddy　current　and　the　principle　of　hydraulic　braking.　In　this　novel　HER,　both　sides　of　the　rotor　are　used　for　hydraulic　braking,　and　the　outer　ring　of　the　rotor　generates　eddy　currents.　The　finite　element　models　of　the　flow　field　and　the　electromagnetic　field　are　established　separately　and　solved　by　computer　to　predict　the　braking　torque　of　the　EHR.　The　prototype　was　developed　and　the　braking　performance　of　the　EHR　was　obtained　through　the　bench　tests.　Comparing　the　theoretical　calculation　results　and　experimental　data,　the　braking　characteristics　of　the　EHR　are　analyzed.　At　low　speed,　the　EHR　mainly　relies　on　the　eddy　current　braking,　whereas　at　high　speed,　it　relies　on　both　eddy　current　and　hydraulic　braking.　Moreover,　the　control　of　the　EHR　can　be　realized　only　by　adjusting　the　braking　torque　of　the　eddy　current　part,　which　simplifies　the　control　system.