Taking the cooling exhaust gas discharged from the outlet of sinter waste heat boiler as the heat source fluid of low temperature waste heat organic Rankine cycle (ORC) system, and according to the selection criteria of thermal cycling characteristics, environmental protection and security of working fluid, the R245fa, R600, R601 and R601a were selected as the organic working fluids of ORC system. The effects of evaporation temperature and condensation temperature of different working fluids on the thermal performance of ORC system were analysed numerically. The research results show that the net output work of ORC system first increases and then decreases with the increase of evaporation temperature, and the ORC system could obtain the maximum net output work through the adjustment of evaporation temperature. When the evaporation temperature of working fluid is larger than 110 ℃, the net output work of R600 is the maximum, and on the contrary, the net output work of R245fa is the maximum. The thermal efficiency of ORC system increases with increasing the evaporation temperature. The variations of exergy efficiency with the evaporation temperature for different working fluids are also different. The exergy efficiency of R600 is the maximum for the ORC system, and the corresponding evaporation temperature is 125℃. The net output work, thermal efficiency and exergy efficiency of ORC system all decreases with increasing the condensation temperature of working fluid. For a given operating condition of ORC system, the thermal efficiency of R601 is the maximum, and the thermal efficiency of R245fa is the minimum.