The atomic and electronic structure of the beta-silicon nitride (beta-Si3N4) crystal have been determined using the ab initio pseudopotential method based on the density functional theory. We have obtained the stable lattice parameters and the stable positions of 14 atoms in the unit cell for the structure P6(3)/m for the first time. The electronic structure and the charge distribution indicate that the Si-N bond has both ionic and covalent characters. The band structure is in good agreement with the other first-principles results and consistent with the experiments.