Abstract: Flue gas discharged from end outlet of LR6A3L diesel engine was taken as research object，mass flow and temperature of flue gas were 540 kg/h and 330 ℃.Based on organic rankine cycle（ORC）system，R123，R245fa and R600 were selected as organic working fluids，and effect of evaporation temperature on ORC system thermal performance were studied.Results showed that with increase of evaporation temperature，system net output power，cycle thermal efficiency and exergy efficiency all gradually increase，and system total irreversible loss gradually decreased.When system operating condition was certain，net output power，cycle thermal efficiency and exergy efficiency of R123 were the maximum，and total irreversible loss was the least.