To improve vehicle engine fuel economy，an organic Rankine cycle (ORC) system was designed to recover waste heat from heavy-duty diesel engines through their exhaust air. R245fa was selected as the working fluid after compared with several other organic fluids. A test platform for waste heat recovery was built, which includes an ORC circuit, an energy conversion and consumption device, a data measure and acquisition unit and a heat supply module. The feasibility of using R245fa as working fluid in the heavy-duty diesel engine ORC system was proved by experiments. The maximum power output of the system is 490W. The experiments indicate that the matching of the expander，the generator and the ORC system is the key factor restricting the power output. The system cycle efficiency increases with the evaporating pressure increase.