Ag/a-C:H nanocomposite film with nanosized Ag particles (about 2–5 nm) embedded in a-C:H matrix is deposited by the medium frequency unbalanced magnetron sputtering. The effects of vacuum atomic oxygen and ultraviolet radiations on the composition, microstructure, morphology and vacuum tribological properties of the Ag/a-C:H nanocomposite film have been investigated. Results show that the radiations can induce the oxidation and decomposition of carbon matrix, which lead the high Ag content nearby surface, the increased sp² carbon content, as well as the reconstruction of microstructure. As a result, the diffusion rate of Ag atoms increases while the connectivity and rigid of the carbon network decrease. The composite film exhibits low friction and high wear performance after radiations.