DLC coatings have great potential in semiconductor manufacturing due to their excellent friction and hydrogen permeation barrier (HPB) properties. However, how H-atom irradiation affects interfacial structure evolution and friction remains unclear, largely due to the limitations of in situ characterization techniques. This study combines molecular dynamics simulations and experiments to investigate the effects of H-atom irradiation on the interfacial structure and frictional properties of Fe substrate/DLC coatings. The hydrogen permeability of DLC is approximately three orders of magnitude lower than that of the Fe substrate (∼10 3), indicating superior hydrogen resistance. H-atom irradiation degrades the friction of the Fe substrate by producing lattice phase transitions and interfacial defects. In contrast, H-atom irradiation enhances the structural order of the DLC coating by modifying the carbon bonding at the interface, improving strain distribution, and reducing local stress concentrations. This strain control improves the durability of the graphene-like six-membered ring structure formed at the friction interface, thus enhancing the DLC friction performance under H-atom irradiation. This study elucidates the atomic-scale mechanisms for hydrogen-induced structural evolution and enhancement of frictional properties in DLC coatings and offers insights into their applications to semiconductor manufacturing.