The hydraulic retarder is an auxiliary braking device used for commercial vehicle in a long slope brake, and its transmission oil generates a lot of heat in its working process. If the heat of transmission doesn’t go through a reasonable management, it will seriously affect the braking performance of hydraulic retarder.To cool down the transmission oil, it will aggravates the load of the engine cooling system, and the long cooling path sometimes causes heat exchange not timely. When the Rankine cycle is used for cooling the hydraulic retarder transmission oil in virtue of its good heat transfer performance in phase change process, it can make the transmission oil temperature controlled more stable. In this new system, the setting parameters of the Evaporate-condensate system will affect the stability of the transmission oil temperature in the hydraulic retarder inlet and the energy recovery efficiency of the system.First of all, the outlet temperature of hydraulic retarder is set according to the stable condition in this paper. Next, it is the heat transfer calculation of evaporator and condenser under the different braking powers of hydraulic retarder. Then the evaporate-condensate system is explored matching characteristics through experimental research and simulation. Moreover the experimental device combined with the ORC is established, narrowing 100 times according to the hydraulic retarder power. Finally, the rationality of system basic parameters is verified in the different braking powers of hydraulic retarder.Experimental results verify the rationality of simulation results. In addition, the paper confirms hydraulic retarder temperature controlled steadily and gets the working medium flow of Rankine cycle in different braking powers.