High performance double-layer coatings composed of copper (Cu) interlayer and the Cu/diamond-like carbon (DLC) composite top layer were prepared via magnetron sputtering for protection of carbon steel. The effect of Cu content in the composite layer on the internal stress, contact angle, mechanical, tribological, and corrosion performance of coatings was discussed. Raman spectroscopy confirmed formation of DLC phase. Double-layer Cu-rich coatings exhibited high degree of sp2 carbon clustering, but low diamond-like sp3 bonding. The internal stress of double layer Cu-(Cu/DLC composite) coatings was decreased with Cu content increase. The double-layer Cu-(Cu/DLC composite) thin films with low Cu content did not pose a significant effect on hardness and Young's modulus of the steel substrate, while increase of Cu content enhanced hardness of coating up to 28 GPa. The contact angle of steel substrate showed an increase when coated with double-layer Cu-(Cu/DLC composite) thin film, but not that much at such inadequate Cu content. Inclusion of Cu interlayer improved to some extent corrosion properties, where increase of Cu content assisted in protection. Double-layer coatings with the highest performance were compared with single-layer Cu/DLC coating. Elimination of interlayer deteriorated mechanical properties, but increased electrochemical performance, signifying the importance of controlling Cu/DLC composition and Cu interlayer inclusion.