Abstract: This study aims to investigate the metallurgical behavior and the transformation mechanism of microcrystalline structure of coke in a hydrogen-rich smelting process. The co-gasification reaction of coke in the reaction gas (CO₂ + H₂O) was studied under different H₂O contents, ranging from 0 to 20vol%. The thermal properties of coke after the gasification reaction were examined using the coke reactivity index (CRI) and coke strength after reaction (CSR) at 1100°C. The microcrystalline structure was analyzed by Raman spectroscopy, and the pore structure was studied by scanning electron microscopy, Brunauer–Emmett–Teller method, and X-ray computed tomography. The results indicated that the CRI increased with increasing H₂O content in the gas, while the CSR decreased. Pore erosion occurred in both the internal and surface parts of the coke gasified with pure CO₂. Furthermore, as the H₂O content increased to 20vol%, the pores at the surface of the coke were significantly eroded. The enlarged pores, thinning pore walls, and generation of pore channels eroded a large number of small pores inside the coke, which results in elevated levels of porosity within the coke. This indicates that the carbon dissolution of H₂O was more pronounced than that of CO₂, ultimately leading to a significant decrease in the strength of the reduced coke. Raman spectra demonstrated that the overall graphitization of the reduced coke increased with H₂O content due to the fact that H₂O primarily erodes the irregular carbon structure, resulting in a relatively higher percentage of its internal regular structure.