An investigation on the post-combustion phenomena in an argon oxygen decarburization (AOD) system containing a converter and a flue has been conducted. An AOD converter is mainly characterized by nozzles installed at the lower side of the converter. The nozzles are intended to inject the decarburization gas of oxygen mixed with an inert gas such as argon. The injection promotes stirring and lowers the partial pressure of CO in the converter. For the AOD converter of interest in the current work, a fan is installed in the end of the AOD flue to help extract the off-gas from the converter. The influence of different fan gauge pressures as well as temperatures of the gas mixture, containing the generated CO and argon, on the post-combustion in the whole AOD system was studied. The realizable k–ϵ model was employed as the turbulence model. In addition, the reaction and radiation were also taken into account by use of the species transport model and the discrete ordinate model. It was indicated from the modeling results that the post-combustion was only present in the flue for the present modeling conditions. Moreover, a critical fan gauge pressure was found, which could yield a maximum post-combustion in the flue gas. Finally, no obvious change on the post-combustion was shown if the inlet gas mixture temperature was varied between 1500 and 1700°C.