Abstract: Heavy-duty vehicles are generally equipped with non-contact hydraulic retarders or eddy current retarders to ensure safe driving during long downhill conditions. The hydraulic retarder (HR) has poor low-speed characteristics, and it is difficult to meet the needs of the auxiliary braking system when heavy-duty vehicles are used at low speeds on long slopes. The eddy current retarder (ECR) has low torque at high speeds. The braking performances of these two retarders have complementary characteristics. Based on the principles of the eddy current braking and the hydraulic braking, the two retarders were combined to obtain a radial structure eddy current-hydraulic hybrid retarder (EHR). At low speeds, the EHR mainly relied on the eddy current braking, while at high speeds, it relied on both eddy current and hydraulic braking. The prototype was made for the bench test, and its braking characteristics and control method were studied. A vehicle dynamics model that relied only on retarder's braking was established, and a retarder model considering the response time was established based on the bench test results. In this paper, through the numerical simulation of the above model, the braking characteristics of the EHR, HR and ECR designed in the same space were compared. The study shows that the vehicle only relies on the EHR for braking, which can not only meet the national standard's requirements for its auxiliary braking systems, but also minimize the braking time. Additionally, the vehicle's constant speed control can be achieved only by adjusting the braking torque of the eddy current part, which simplifies the control system.