This paper aims to study the effect of low nitrogen doping on the microstructure and mechanical properties of hydrogenated diamond-like carbon films. By using unbalanced magnetron sputtering and plasma enhanced chemical vapor deposition (PECVD) composite technology, tungsten carbide transition layer and hydrogenated diamond-like carbon films with different nitrogen content (a-C:H(N)) were prepared on 316 stainless steel and silicon substrates. The microstructures of the films were characterized by Raman spectroscopy, X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The hardness and residual stress of the films were characterized by micro and nano mechanical comprehensive measurement system and film stress measuring instrument. Results show that with nitrogen doping, carbon-nitrogen bond (CN) was formed in the films and mainly existed in the form of C=N bond, and the ratio of C=N/CN decreased with the increase of nitrogen content. When the nitrogen content increased from 0 to 0.12 at%, the ID/IG ratio of the film decreased rapidly, the ratio of sp²C=C/sp³C-C decreased from 0.65 to 0.563, whereas the hardness of the films remained unchanged at about 20.4 GPa, and the residual stress decreased from 3.35 GPa to 1.31 GPa. With the increase of nitrogen content, the ratio of sp²C=C/sp³C-C increased, the hardness of the films decreased rapidly, and the residual stress decreased slowly. The effect of nitrogen doping on the microstructure of DLC films has a critical value of 0.12 at%. When the amount of nitrogen doping is lower than this value, it promotes the formation of sp³ hybridization, and the film has high sp³ hybridization, while the sp³ hybridization of the films decreases with the increase of nitrogen, and the sp³ hybridization decreases. The films with higher hardness and lower residual stress can be obtained with low nitrogen doping.