Based　on　Water-cooled　Permanent　Magnet　Retarder　brake　work　of　analysis,　this　paper　put　forward　a　fuzzy　control　method　using　retarder　internal　temperature　error　speed　error　and　the　hand　displacement　of　the　DIP　switch　as　input,　and　increase　the　weighting　factor　alpha　and　beta　to　optimize　the　control　rules.　According　to　the　actual　conditions,　Water-cooled　Permanent　Magnet　Retarder　input　is　adjusted.　Vehicle　test　results　show　this　method　in　the　normal　vehicle　speed,　enable　the　Water-cooled　Permanent　Magnet　Retarder　to　output　stable　and　sub-file　braking　torque;　also　high　speed　retarder　protection　may　be　achieved.