To solve high power consumption and problem of braking torque heat-fade of the conventional eddy current brake, a new active electromagnetic liquid-cooled retarder was proposed based on the principle of eddy current brake and motor energy regeneration brake. The new type of retarder included a liquid cooled eddy current retarder and a single-phase switched reluctance motor with an outer rotor. The mathematical model of electromagnetic field for the retarder was established. The braking performance of the retarder was predicted by numerical simulation, the opening and closing angle of the switched reluctance motor were optimized, and the energy recovery power of the the switched reluctance motor in the downhill continuous braking, the energy recovered in the emergency braking and start torque at low speed were calculated. At last, tests for the air loss moment, heat-fade of braking toque, power generation performance and power-driven performance were carried out. The test results showed that the eddy current braking torque reached 1260N·m at 1000r/min. The braking torque was declined by 15% in the continuous braking stage. The braking torque of the motor was increased at first and then decreased with the increase of speed. When the speed was 1000r/min, the braking torque of the motor reached the maximum;when the vehicle was slowed down at speed of 35km/h, the recovery power was up to 94kW.