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The tribological behavior of hydrogenated and hydrogen free diamond like carbon (DLC) coatings sliding against Al₂O₃ in air and pure water was investigated by ball-on-disc reciprocation wear test, and the effect of hydrogen was discussed. The results showed that in air environment, the Al₂O₃ slide against DLC under solid lubrication condition, and the wear of DLC coatings was mainly affected by coating mechanical properties. The hydrogen lowered the coating hardness and brought more DLC wear in air environment. In water environment, the solid lubrication effect is weak, the hydrogen began to play an important role in DLC wear. The hydrogenated DLC coating with saturated ‐CH bonds showed better wear resistance even though its hardness is lower. The hydrogenated DLC coating with unsaturated ‐CH bonds was easy to graphitize and generate massive wear no matter in water or in air environment.