Abstract: The effect of hydrogen injection on blast furnace operation and carbon dioxide emissions was simulated using a 1D steady-state zonal model. The maximum hydrogen injection rate was evaluated on the basis of the simulation of the vertical temperature pattern in the blast furnace with a focus on the thermal reserve zone. The effects of blast temperature and oxygen enrichment were also examined to estimate coke replacement ratio, productivity, hydrogen utilization efficiency, and carbon dioxide emission reduction. For blast temperature of 1200°C, the maximum hydrogen injection rate was 19.0 and 28.3 kg of H₂/t of hot metal (HM) for oxygen enrichment of 2vol% and 12vol%, respectively. Results showed a coke replacement ratio of 3–4 kg of coke/kg of H₂, direct CO₂ emission reduction of 10.2%–17.8%, and increased productivity by up to 13.7% depending on oxygen enrichment level. Increasing blast temperature further reduced the direct CO₂ emissions. Hydrogen utilization degree reached the maximum of 0.52–0.54 H₂O/(H₂O + H₂). The decarbonization potential of hydrogen injection was estimated in the range from 9.4 t of CO₂/t of H₂ to 9.7 t of CO₂/t of H₂. For economic feasibility, hydrogen injection requires revolutionary progress in terms of low-cost H₂ generation unless the technological change is motivated by the carbon emission cost. Hydrogen injection may unfavorably affect the radial temperature pattern of the raceway, which could be addressed by adopting appropriate injection techniques.