Abstract: A series of Si and N co-incorporated DLC (Si/N-DLC) coatings were deposited using plasma enhance chemical vapor deposition (PECVD) technology under varying SiH₄/N₂ flow ratios, and the dependence of the coatings’ microstructure, mechanical properties and tribological behavior in oilfield produced water environment on the SiH₄/N₂ flow ratio was investigated, focusing on the lubrication and failure mechanisms in the oilfield environment. The results demonstrated that the Si/N-DLC coatings exhibited high-quality surface and cross-sectional morphologies, with smooth surfaces (R_a: 0.97~2.00 nm) and no micro-defects or cracks. As the SiH₄/N₂ flow ratio decreased, the Si content in the coating gradually decreased (from 6.98% to 0.00%), while the N content gradually increased (from 0.00% to 6.37%). This compositional change induced a structural transformation of the coating from sp³ to sp² bonding. Consequently, the hardness and elastic modulus decreased overall, whereas the toughness and adhesion strength were significantly improved, attributed to the formation of strong covalent bonds between C and N within the coatings. The Si/N-DLC coatings substantially enhanced the tribological performance of the 316L SS substrate in oil field environments. The friction coefficient and wear rate exhibited a decreasing-then-increasing trend with decreasing SiH₄/N₂ flow ratio. Notably, the Si₆₀/N₄₀ coating system achieved a low friction coefficient of 0.024 and an ultra-low wear rate of 1.80×10^–8 mm³/N·m). The lubrication mechanism was attributed to the formation of a solid-liquid composite lubrication system with the oil field produced water. In the mixed lubrication state, the synergistic effect of the liquid film on the coating surface and the graphitized transfer film on the wear scar surface not only shifted the frictional shear interface, but also effectively hindered material transfer (further wear) at the friction interface. This synergy significantly reduced the friction coefficient of the coating and enhanced its wear resistance. For Si/N-DLC coatings deposited at higher (Si₁₀₀/N₀) and lower (Si₂₀/N₈₀ and Si₀/N₁₀₀) SiH₄/N₂ flow ratios, the dominant wear mechanisms were abrasive wear and corrosive wear, respectively, both exhibiting higher wear rates and even failure. These findings provided valuable insights for advancing the application of DLC coatings in tribological protection under oil field conditions.