Abstract: In this work, a mathematical model has been developed by means of theoretical analysis for the oxygen top-bottom combined blowing process, in which a gas-stirred is injected through the tuyere at the center of the vessel bottom, in a hot model with 100 kg capacity. By use of this model, the changes of temperature and compositions of metal bath can be estimated. The results calculated by the model have been in good agreement with the experimental data obtained in hot model experiments.