Microstructure and adhesion properties of nitrogen-doped diamond-like amorphous carbon (DLC) film deposited by r f plasma-enhanced chemical vapor deposition method is studied by atomic force microscope, Auger electron spectroscopy (AES) and micro-indentation analysis. Results show that, with the increase of nitrogen content, particles of tens of nanometer in size appear in the film. The atomic lateral force microscope and AES analyses show that these nano particles are nitrogen-rich amorphous carbon nitride CNx, where x is larger than 0.126. Micro-indentation measurement shows that this DLC/CNx nano-composite structure reduces the residual stress of the film and improves the adhesion between DLC film and Si substrate.