In this study, we prepared a-C:H films with different nanostructures at different methane flow rates. The effect of the methane flow rate on the tribological proper ties of 440 steel/a-C:H friction pairs and a-C:H:Ti/a-C:H friction pairs in an atmo spheric environment was studied by a reciprocating friction machine. The results show that there is no relationship between the tribological properties of 440 steel/a C:H friction pair and methane flow rate. The tribological performance of the a-C:H: Ti/a-C:H friction pair was greatly improved. In particular, in the friction pair of a-C:H: Ti/a-C:H with a methane flow rate of 20 sccm, superlubricity is shown, and the wear rate is only 4.04 10 9 mm3 /Nm. After tribological experiments, Raman spectros copy, XPS, and other characterization methods were used to study the relationship between the nanostructure and tribological properties of a-C:H:Ti films and a-C:H prepared with different methane flow rates. This study is great significance to the application of a-C:H:Ti/a-C:H friction pair in mechanical parts under atmospheric environment