Abstract: Given the unclear mechanism of multi-stage coal-oxygen injection and combustion in high-viscosity molten bath within iron bath smelting reduction furnace, this study established a three-dimensional transient numerical model that coupled the volume of fluid（VOF） multiphase flow, species transport, and the eddy dissipation model （EDM） for combustion. The study systematically analyzed the multiphase flow field structure at the lance outlet, temperature distribution, and the burnout behavior of pulverized coal under oxygen concentrations ranging from 25% to 100% and various coal-to-oxygen ratios. The results indicate that the high-viscosity, high-density bath environment significantly suppresses the momentum transfer of the jet, leading to the formation of a characteristic "confined recirculation zone" （resembling an S-shape） at the lance exit region, rather than a typical free jet. While this flow-field structure enhances gas-solid mixing, it simultaneously impedes convective heat diffusion, resulting in a localized region of high thermal load （hot spot） near the lance exit. The synergistic action of the upper and lower oxygen lances in the multi-stage injection reactor elevates the temperature of the oxidation zone. Oxygen concentration is the primary controlling factor determining the combustion efficiency of pulverized coal. As the oxygen mass fraction increases, the average bath temperature and the volume of CO₂ generated increase significantly, with the pulverized coal burnout rate reaching a maximum of 82.59%. In contrast, variations in the pulverized coal injection rate exert lesser influence on the burnout rate. Considering both combustion efficiency and lance longevity, while high oxygen content operation can significantly enhance the burnout rate, careful attention must be paid to the risk of nozzle ablation caused by localized overheating. This study elucidates the coupling mechanism of combustion and heat transfer under confined jets, providing a theoretical basis for optimizing oxygen supply strategies and extending lance service life in industrial applications.