Thermal performance values of 41 working fluids in a trans-critical organic Rankine cycle (ORC) driven by waste heat flue gas of 473.15 K were calculated by means of a theoretical model in which the inlet and outlet temperatures of flue gas were fixed and therefore the thermal efficiency and net work output were unified into one parameter as long as the heat absorbed was given. The influences of pinch point temperature difference (PPTD) in the evaporator and working fluid properties on cycle performance were analyzed. Calculation results showed that for fluids with critical temperature Tc<Tgas

out

and fluids with Tc>0.88Tgas

in

Tc had dominant influence on thermal efficiency. For fluids with Tc between Tgas

out and 0.88Tgas

in

fluid dryness had significant influence on cycle performance

and wet fluids outperformed dry fluids apparently. Wet fluids with Tc between Tgas

out and 0.88Tgas

in exhibited the highest thermal efficiency. For fluids with Tc>0.88Tgas

in

PPTD might lie either inside the evaporator or at the outlet. Thermal performance values of the cycle with PPTD inside the evaporator outperformed that with PPTD at the outlet. Application of such conclusions was confirmed through sensitivity analysis for flue gas inlet and outlet temperatures.