Abstract: The choice of working fluid of Organic Rankine Cycle plays a key role in system efficiency and system design.The HFC-245fa used in the past cannot meet the environmental protection requirements put forward by the international community because of its GWP of 1 030.This paper summarizes the comparison of physical properties and system performance between HFO-1336mzz(Z) and HFC-245fa.The results show that the GWP=2 of HFO-1336mzz(Z) meets the requirements of environmental protection.It has higher critical temperature and lower critical pressure in physical properties,which is enough to work at higher evaporator temperature.In many theoretical and experimental studies on HFO-1336mzz(Z) and HFC-245fa,the pump power consumed by HFO-1336mzz(Z) in ORC system is lower than that consumed by HFC-245fa system under the same working condition,and the net cycle efficiency is also improved.Adding a regenerator will make HFO-1336mzz(Z) ORC system have greater advantages.Therefore,HFO-1336mzz(Z) has better performance and development prospect in ORC system.