(VNbTa)N x films with different nitrogen contents (x = 0-0.67) were deposited at 250 °C by reactive magnetron sputtering by varying the N 2 flow ratio ( f N) from 0% to 25%. The undoped film exhibited a BCC solid-solution structure with low hardness and modulus, while nitrogen incorporation induced a transition to a single FCC phase for x = 0.25–0.67. The film with f N = 20% (x = 0.48) showed an optimal property combination: a high hardness of 55.10 GPa, an H/E ratio of 0.10, excellent fracture toughness, and a low wear rate of 15.88 × 10 -6 mm 3·N -1·m -1. Such enhancements are attributed to antisite defects (TM-N) in the sub-stoichiometric nitride, where metal atoms occupy nitrogen sites. XPS results indicated a higher electronic density near d-t 2g(Me) states relative to p(N)-d-e g(Me) hybrids, elucidating the electronic origin of the performance improvement. This work demonstrates that controlled nitrogen doping is a viable route to fabricate super-hard and tough medium-entropy nitride coatings for advanced protective applications.