Abstract: Copper-nickel (Cu-Ni) alloy has received extensive attention because of its high corrosion resistance and remarkable physical properties. Cu-Ni alloy is widely applied to solar cells, power plants and electrical sliding contacts, etc. At present, the studies of Cu-Ni alloy concentrate on the macroscopic level, while the deformation mechanisms at the atomic level are studied rarely. Meanwhile, with the rapid development of micro/nanodevices, it is critical to investigate and disclose the nano-sized tribological properties and deformation mechanisms. This paper aimed to understand nano-tribological behaviours and deformation process of Cu-Ni alloy, because studying the distribution of atomic, lattice change and stress propagation at the atom scale could help to understand the deformation mechanism of Cu-Ni alloy. This research based on molecular dynamics simulation, the sliding friction models of diamond rough abrasive ball and Ni60/10%Cu (C1), Ni60/20%Cu (C2) copper-nickel alloy were established. The sliding friction behavior of diamond abrasive grains at different friction depths, combined with the wear morphology, number and distribution of wear atoms, friction force and subsurface damage of the alloy, the wear mechanism of the alloy under nano-size were studied. The results showed that in the friction process, the alloy wear atoms first accumulated in front of the abrasive particles. With the progress of sliding friction, when the indentation depth was 10 Å, the adhesion force between the wear atoms and the abrasive particles was small, and the wear atoms flowed to the wear scar. On both sides, when the indentation depth was 20 Å, the number of wear atoms increased, and the increased wear atoms were mainly accumulated in front of the abrasive particles to wear the alloy together. In addition, it was also observed that the morphologies of wear debris accumulated on the surface of the alloy were asymmetric. With the increase of indentation depth, the dislocation density of the alloy increased during the friction process, and the degree of subsurface damage of the alloy increased. Although there were some differences in the force between C1, C2 alloys and abrasive particles at different indentation depths, the change trend of the force between the two was consistent. However, at the same indentation depth, the average dislocation density of C2 alloy was larger than that of C1 alloy, and the subsurface quality of C1 alloy was better than that of C2 alloy. This indicated that the friction depth was an important factor affecting the subsurface quality of the alloy, and the increase in the number of Cu atoms would increase the subsurface damage of the alloy during nano-size friction. Moreover, with increasing the friction depth, more plastic deformation and lattice defects were generated. This work provided a new viewpoint to understand nano-tribological behavior and deformation mechanism in nano friction process, and offered a theoretical basis for the engineering application of Cu-Ni alloy.