A mathematical model of subcritical organic Rankine cycle(ORC) system is established for the flue gas waste heat of 120～150 ℃. Firstly

the thermal performance and economic performance of the system are analyzed at different heat source temperatures by taking R245fa as an example. Then

a multi-objective optimization study is conducted for six pure working fluids based on NSGA-Ⅱ algorithm. At last

working fluid selection and performance analysis of the ORC system with various heat source temperatures are carried out by TOPSIS method and gray correlation analysis. The results show that

in the temperature range of this study

the increase of superheat degree and evaporator pinch point temperature difference is not conducive to improve the system performance. The optimal working fluids are varied at different heat source temperatures

when the heat source temperature is 120 ℃

R601has the best thermal performance

R245fa has the best economic performance and R1233zd has the best overall performance. The increase of heat source temperature is beneficial to improve the economic performance of the system. The optimal evaporation temperature of each working fluid increases with the heat source temperature. The gray correlation analysis indicates that the comprehensive performance of all six working fluids improves with the heat source temperature.