The work aims to study the effect of N2 flow ratio (R=N2/(Ar+N2)) on structure and mechanical and tribological properties of molybdenum nitride (Mo-N) coatings by DC reactive magnetron sputtering. Mo-N coatings were deposited on 304 stainless steel substrates by DC reactive magnetron sputtering. The structure, surface morphology and wear morphology, micro-hardness, adhesion strength, friction and friction and wear properties of Mo-N coatings were analyzed, characterized and evaluated by SEM, XRD, Vicker microhardness meter, Rockwell indenter and ball-on-disk tribometer, respectively. With the increase of nitrogen flow ratio (R) from 0.3 to 0.7, the coating was mainly composed of γ-Mo2N face-centered-cubic (fcc) phase. When R was 0.7, a small volume of δ-MoN hexagonal phase appeared in the coating. The microhardness of the coating decreased first and then increased, and the maximum hardness reached 3060HV. The adhesion strength of the coating first increased and then decreased. When R was 0.4 and 0.5, the coatings exhibited higher adhesion strength (40 N) and better tribological properties. The average friction coefficient was about 0.22 and the coating wear was mainly abrasive wear. For the coating prepared on 300 ℃ substrate temperature, N2 gas flow ratio (0.3~0.7) has a little effect on the phase structure of the coating when changing between 0.3~0.7. When the hardness is relatively high, the better adhesion strength is, the better tribological properties are.