In order to achieve low-carbon transition in the iron and steel industry, the reduction process and carbon deposition behavior of iron ore concentrate pellets in hydrogen-rich atmosphere [H₂, CO, and CO-H₂ mixtures] were studied in this paper. By combining thermodynamic calculations with high-temperature in-situ X-ray diffraction (XRD), the phase change pathways and thermodynamic characteristics of pellets under different atmospheres and temperature conditions were systematically analyzed. The results indicate that the reduction rate of H₂is significantly higher than that of CO, and the utilization efficiency of reducing gas increases with temperature and higher H₂ proportions. Carbon deposition is prone to occur within the temperature range of 400–800?°C in a CO atmosphere, while carbon precipitation is suppressed when temperature is above 900?°C; the formation of Fe₃C depends on both the carbon potential of the atmospheres and temperature, and high CO partial pressure and low oxygen are favorable conditions. This work provides a theoretical basis and experimental support for the optimization of hydrogen-based direct reduction processes.