Diamond-like carbon (DLC) films are regarded as highly competitive surface films for marine service environments owing to their excellent lubricity, wear resistance, and corrosion protection. In this work, a series of (NbTaMoWAl) x-DLC films were developed by systematically tuning the multi-element co-doping levels. We investigated its effects on microstructural evolution and tribo-corrosion mechanisms. At low doping levels ( ~ 4   at.%), high-entropy additions promoted the formation of a stable carbonate-type passive film and preserved high compactness with the sp 3 carbon network, thereby increasing the charge transfer resistance ( R ct), lowering the friction coefficient, and suppressing the tribo-corrosion failure. With further enrichment in high-entropy content (~ 12, 24, 35   at.%), the films exhibited intrinsic features of carbide ceramics: increased columnar gaps and grain-boundary channels and stronger interfacial galvanic effects. It led to the OCP shifting toward more negative values, and the COF showed larger fluctuations. Such microstructural evolution caused by excessive high-entropy doping accelerated the penetration of corrosive media along columnar grain boundaries and channels, thereby undermining the overall protective efficacy.