Hydraulic retarder, as an auxiliary braking device, is widely used in commercial vehicles. Nowadays, the hydraulic retarder’s internal oil is mainly cooled by the coolant circuit directly. It not only aggravates the load of engine cooling system, but also makes the abundant heat energy not be recycled properly.In this study, an independent energy supply device with organic Rankine cycles is applied to solve the problems above. In the structure of this energy supply device, the evaporator’s inlet and outlet is connected in parallel with the oil outlet and inlet of the retarder respectively. A part of oil enters the evaporator to transfer heat with the organic fluid, and the rest of oil enters the oil-water heat exchanger to be cooled by the coolant circuit. According to the different braking conditions of the retarder, the oil temperature in the inlet of the hydraulic retarder can be kept within the proper range through adjusting the oil flow rate into the evaporator properly.Firstly, the temperature and flow characteristics of hydraulic retarder’s internal oil are studied. Secondly, the steady-state heat transfer model of the energy supply device is established, and the distribution principle of the oil flow rate between the evaporator and the oil-water heat exchanger is proposed in order to improve the temperature stability of the energy supply device and stabilize the oil temperature in the retarder’s inlet. At last, with the multiple comparisons with the conventional structure of hydraulic retarder, comprehensive analysis of the energy supply device’s effect mechanism on the working stability of the retarder is carried out.Result shows that although this additional device increases the cost and the space requirement of the whole hydraulic retarder, it greatly improves the working stability of hydraulic retarder, and it also recovers the transmission oil’s waste-heat effectively, which reduces the energy consumption as well as the cooling load of engine cooling system.