In extreme deep-sea environments, the synergistic effect of high hydrostatic pressure and alternating loads induces a mechanical-electrochemical coupling effect, exacerbating surface abrasion and corrosion damage on moving components, thereby seriously threatening the long-term safe operation of equipment. Amorphous carbon (a-C) coatings have attracted extensive attention due to their combined excellent lubrication, friction reduction, and corrosion resistance. Among them, the graphitization/passivation coupling modification strategy can effectively regulate tribological behavior while maintaining the intrinsic structural integrity of the coating, showing promising application prospects. In this study, based on theoretical calculations, we systematically investigated the effects of different degrees of graphitization/passivation coupling treatment on the interfacial structure and friction properties of a-C coatings. The simulation results indicate that at a relatively low degree of graphitization, the friction coefficient exhibits a non-monotonic trend with increasing surface hydrogen content; meanwhile, increasing the degree of graphitization further reduces the friction coefficient, confirming the effectiveness and feasibility of the graphitization/passivation coupling strategy for friction reduction in marine environments. On this basis, experimental verification was carried out. Surface graphitization‑modified a‑C coatings were prepared via laser irradiation, and the degree of surface passivation was further regulated by varying the hydrogen flow rate during deposition. The results show that with increasing hydrogen flow rate, the I_D/I_G ratio gradually decreases while the sp³‑hybridized carbon content increases, indicating densification of the carbon network structure. Time‑of‑flight secondary ion mass spectrometry (TOF‑SIMS) further reveals that hydrogen and hydrocarbon species are mainly enriched in a surface layer of about 80 nm in thickness, forming an obvious hydrogen‑rich layer; the increase in hydrogen content is mainly attributed to the contribution of hydrocarbon groups (CH_x), while the proportion of isolated hydrogen atoms remains nearly constant. Deep‑sea abrasion‑corrosion tests show that under low‑hydrogen passivation conditions, the variation in friction performance with increasing passivation degree agrees well with the simulation predictions. Although the coating maintains a low friction coefficient under low‑hydrogen passivation, surface microcracks and structural defects easily become fast penetration channels for corrosive ions such as Cl^-. In contrast, increasing the hydrogen content effectively saturates the dangling bonds of carbon atoms, forming a denser amorphous carbon network, thereby suppressing corrosion ion diffusion and significantly improving corrosion resistance. The relevant results provide a reliable basis for the optimal design of long‑term protective coatings for deep‑sea environments.