The electronic structure of the Sigma 5(210) grain boundary in silicon was calculated by the first-principles, self-consistent, linear muffin-tin orbitals/tight-binding representation method on the basis of the atomic structure simulated by the bond orbital model. The calculated electronic structure is found to have localized and resonant defect states, which are caused by the distortions of the atomic structure at the grain boundary. Sharply localized states in the pseudo-gap were observed along with splitting of s states and dissipation of s-p mixed states. A rehybridization effect was revealed at the grain boundary on the atoms with strongly distorted bonds. However, there are no states inside the band gap. The increase of the s-state occupancy in comparison with the p-state occupancy appeared on the atoms with strongly distorted bonds at the grain boundary. The relationship between local electronic structure and local arrangement of the atoms is discussed.