With the improvement of occupants’ awareness on the driving safety, hydraulic retarder applications increase quickly. The traditional hydraulic retarder, on the one hand, exhausts the waste heat of transmission oil by the engine cooling system; on the other hand, the engine power should be consumed to drive the water pump and the engine cooling fan for maintaining the normal operation of the auxiliary braking system.In this study, the Organic Rankine Cycle (ORC) instead of the traditional hydraulic retarder water-cooling system is applied to achieve the effective temperature control of the hydraulic retarder, while the waste heat of transmission oil could be recovered for saving vehicle energy consumption.The ORC fluid selection needs comprehensive consideration for the net power of the ORC and the optimal temperature range of the retarder transmission oil at both the inlet and outlet end, which is the key issue to ensure the stability and efficiency of the ORC system performance.In this study, the brake mechanism and the performance of the hydraulic retarder are analyzed, combined with long downhill driving conditions. The variation characteristics for the circulation flow rate and the inlet and outlet temperature of the transmission oil are determined. The thermodynamic model of theORC is established. There are six fluids are selected as the candidate working fluids after the comprehensive consideration of their thermophysical properties, safety, environmental friendship and related factors; then thermal parameters and thermal performance are calculated and analyzed. After that, performance comparisons on working fluids evaporation pressure, mass flow, net power, thermal efficiency and exergy destruction rate at same evaporation and condensation temperature and operating condition of hydraulic retarder are conducted. Safety levels and environmental impacts were also evaluated. The outcomes indicate that the R141b manifest slightly higher thermodynamic performances than the others for hydraulic retarder waste heat-recovery applications; however, the R601 has the minimum mass flow, and it is the most environment-friendly working fluids. Finally, the evaluated method of working fluid selection is clarified and the optimal ORC working fluid for hydraulic retarder thermal management system is determined.