The hydraulic retarder is an important auxiliary braking device. With merits such as its high braking torque, smooth braking, low noise, long service life and small size, it is widely used on modern commercial vehicles. Transmission fluid of traditional hydraulic retarder is cooled by engine cooling system, which exhausts the heat directly and need additional energy consumption for the thermal management component. On account of the working characteristics of hydraulic retarder, this study designs a set of waste heat recovery system based on the Organic Rankine Cycle (ORC). Under the premise of ensuring stable performance of hydraulic retarder, waste heat energy in transmission fluid is recycled to supplement energy requirements for cooling system. First of all, a principle model, which is scaled down according to D300 retarder`s thermal power generation ration of 1:100, is established. Then through theoretical calculations, components' structural parameters of the ORC are determined. And theoretical model concerning waste heat recovery system based on the ORC is established. Next, through theoretical calculation, the characteristic of waste heat recovery under typical working conditions of hydraulic retarder is determined. What’s more, through simulation of the retarder's working conditions, the waste heat recovery test rig based on the ORC is established. Then, heat recovery characteristic under typical working condition are obtained by analyzing the experimental data. And mathematical model is thus amended. Finally, based on the corrected mathematical model and setting driving conditions, actual effects of total vehicle waste heat recovery system are evaluated. Research shows that the waste heat recovery system can ensure transmission fluid temperature stable from 80 to 120 °C when the hydraulic retarder is working and recover about 6% of the waste heat under the typical working conditions of hydraulic retarder.