Converter gas is a valuable fuel in the converter steelmaking process, and NOx and CO emissions are high due to the high temperature combustion and the absence of H2O vapor. The effects of H2O vapor concentration and the inlet temperature of converter gas on NOx and CO emissions in the combustion are investigated by a detailed chemical reaction mechanism. CO emission decreases sharply when C-H2O,C-inlet increases from 0 to 0.4%. At C-H2O,C-inlet > 0.4% and T-inlet < 950 K, for the reduction of CO emission, the inlet temperature of converter gas is predominant over that of H2O vapor in air. The inlet temperature of converter gas has noticeable influence on NO emission at C-H2O,C-inlet < 2%. With the increase of C-H2O,C-inlet, NO emission first increases, then reaches a peak value, finally decreases. At T-inlet > 1050 K and C-H2O,C-inlet > 2%, NO emission noticeably decreases with C-H2O,C-inlet. In the presence of H2O, H and OH free radicals are easily formed, the reduction path of NO is as follows: NO -> NH/HNO -> N-2.