In top-blown oxygen converter steelmaking process, a large amount of high-temperature off-gas is produced, and the off-gas is a precious valuable fuel containing high concentration of carbon monoxide (CO). Numerical model is developed for top-blown oxygen converter off-gas formation, the off-gas formation is simulated using the developed model, and the influences of the operating model of converter on the characteristics of off-gas (concentrations, temperature, flowrate and sensible heat flux) are investigated. The simulated results indicate that CO concentration varies gently, CO concentration can reach about 80% during 10-80% blowing oxygen time, the change trend of CO(2) concentration is contrary to that of CO concentration during 0-90% blowing oxygen time, and the dramatic changes of oxygen lance height result in significant fluctuations of off-gas flowrate. The operation model of oxygen-blowing pressure significantly affects off-gas sensible heat flux, and the sensible heat flux is high during 40-80% blowing oxygen time. (C) 2011 Elsevier Ltd All rights reserved.