A comprehensive analysis of the crystal structure of n-diamond has been carried out based on a hydrogen-doped (H-doped) diamond model using first principles calculations. In particular, hydrogen concentration dependent elastic constants and lattice parameters for the H-doped diamond have been analyzed. Our results indicate that when the hydrogen concentration is less than 19 at.%, the H-doped diamond is mechanically stable. When the hydrogen concentration is about 4 at.%, the optimized lattice parameter, simulated XRD pattern and electronic properties for the H-doped diamond are all agree well with the corresponding experimental values of n-diamond. The results imply that the n-diamond is likely to be an H-doped diamond. (C) 2011 Elsevier B.V. All rights reserved.