By theory calculation, a new orthorhombic form of diamond has been proved to exist. In this work, the orthorhombic diamond is clearly observed in the multiarc ion-plated varying-C VN films and the effect of C content on the microstructure, mechanical and tribological properties of varying-C VN films were studied in detail. The C doping results in the mechanical and tribological propertie's improvement, together with the decrease of surface roughness and residual stress, and with the increase of C content, the scratch-resistance and wear-resistance capacities increase. The orthorhombic diamond phase only appears in VCN film with 10.97 at.% C, leading to that this VCN film has a relative low room-temperature friction coefficient (similar to 0.56) compared with other films (similar to 0.70), due to the easy-shear layered atomic structure. The VCN film containing 19.14 at.% C with the highest H/E and H-3/E-2 ratios of 0.052 and 0.091 GPa has the minimum wear rate (0.53 x 10(-14) m(3) N-1 m(-1)), 82% lower than that of VN film (2.89 x 10(-14) m(3) N-1 m(-1)), due to the valid assembly of VN, VC and amorphous C phase with perfect balance of hardness and toughness. However, against Al2O3 grinding ball, the main wear mechanisms of all varying-C VN films are adhesive wear and oxidative wear.