Abstract: To reuse the diesel engine of waste heat in exhaust,organic Rankine cycle(ORC) was proposed.R245fa(1,1,1,3,3-pentaflu-oropropane) was used as the working fluid in the ORC system.Final exhaust temperature,net work and actual efficiency of ORC were studied under different evaporating temperature and cooling temperatures.The results show that primary expansion system should be selected when the evaporating temperature is lower than 367.46 K.However,when the evaporating temperature is higher than 367.46 K but lower than 404.6 K,two-level expansion system is recommended.For a fixed cooling temperature,final exhaust temperature is decreased,but net work and actual efficiency of ORC are increased with the increase of the evaporating temperature.Under a given evaporating temperature,final exhaust temperature is decreased,but net work and actual efficiency of ORC are increased with the decrease of cooling temperature.