The hydraulic retarder is an auxiliary braking device generally equipped on commercial vehicles. Its oil temperature change influences the brake performance of hydraulic retarder. The Organic Rankine Cycle (ORC) is a good means to recover exhausted heat. Moreover, it can cool oil and stably control oil temperature with the help of heat absorption related with evaporation. Comprehensively considering the heat-producing characteristics of hydraulic retarder and the temperature control demand, the aimed boundary conditions are determined. Also the changing rules about the working medium flow rate are obtained. In this work, the heat-producing properties of hydraulic retarder under different conditions and the oil external circulating performance is firstly analyzed. By researching the system’s adaptation to the limiting conditions, the aimed temperature to control is prescribed. Then combined with the existing ORC structure, the variation of evaporation temperature and working medium flow rate in the evaporator is disclosed. On the basis, the energy consumption of the pump and the cooling fan is calculated. By comparing the simulation results between the ORC system and the traditional water-cooling system, the temperature control stability, the system energy consumption and the braking torque characteristics of the hydraulic retarder are compared and contrasted. The experiment proves the effectiveness of the oil temperature control by using the ORC system. The results reveal that the ORC system decreases the oil temperature variation by 87% and recovers at least 1kW energy for the vehicle use under the same working condition. Besides it can decrease at most 150N*m braking torque fluctuation. Both the retardant braking stability and the vehicle energy utilization are improved, so the system deserves a future promotion.