Abstract: Cr-Ni-N composite films were deposited on 9Cr18 steel using multi-arc ion plating technology. The effect of N_2 flux on the structure of the films was investigated. The phase compositions of the composite films were examined by means of X-ray diffraction. The tribological properties of the Cr-Ni-N composite films sliding against 9Cr18 steel in vacuum were investigated on a ball-on-disc test rig, using ion-plated Ni, Cr, and CrN films as the comparison. And the cross-section and worn surface morphologies of the composite films were observed using a scanning electron microscope. It was found that the composite films had much higher microhardness and much better wear resistance than the reference films deposited under the same conditions. The compositions and microstructures of the composite films were highly dependent on the N_2 flux. Namely, mono ceramic phase CrN was generated in the composite film at a N_2 flux of 7 sccm, while binary ceramic phases Ni_3N and Cr_2N were produced in the composite films at N_2 flux of 15 sccm and 30 sccm. This accounted for the higher hardness and better wear resistance of the composite films prepared at larger N_2 flux than the one prepared at a small N_2 flux of 7 sccm. Moreover, the better mechanical and tribological properties of the Cr-Ni-N composite films than the ion-plated Ni, Cr, and CrN films were closely related to the nanocrystalline structures.