To improve the poor braking performance of the traditional eddy current retarder, a novel retarder is developed by coupling the eddy current effect and the magnetorheological effect, which has large torque at low speed and stable torque at high speed. To meet the constant speed requirement in the braking process, the indirect adaptive fuzzy H ∞ control strategy is employed to control the rotor speed of the designed retarder. The results show that the proposed retarder has the characteristics of continuously adjustable large torque in full speed section, sensitive control process and constant speed intelligent control.