At present

researches on organic Rankine cycle low-temperature waste heat power generation system mainly have problems such as different evaluation indexes of the system

relatively weak comparability of working fluid

and incomprehensive performance response capability of the system. For the 90～240 ℃ low-temperature waste heat resources

this paper selects the working fluids from the aspects of safety

environmental protection

economy and physical properties of the working fluids. The organic working fluids such as R11

R123

R245fa and R365mfc are selected. The software MATLAB and REFPROP are used to establish mathematical model of the system to study the thermal performance of the system. The results show that

the thermal efficiency and net output of the system are directly proportional to the evaporation temperature and inversely proportional to the condensing temperature. The best evaporating temperature and condensing temperature are 120～140 ℃ and 20～30 ℃

respectively. Hydrofluorhydrocarbons(HFC) has a higher net output power and better environmental performance

and the thermal efficiency of chlorofluorocarbons(CFC) has higher thermal efficiency than other working fluids.Considering comprehensively

R365mfc has the highest net output power and less exergy loss

and is environmentally friendly and safe

which is the optimal refrigerant. The evaporator in each component of the system has the largest exergy loss

then is the condenser and expander

the working fluid pump has the smallest exergy loss.