Numerous materials characteristic including yttrium iron garnet (YIG) are directly dependent on its crystal structure; phase diversity. However, only a few examination of energy and its mechanism at atomistic scales was reported. In this article, a density functional theory (DFT) based calculations have been carried out to study electronic properties of cubic Y3Fe5O12 (YIG) at its known active sites; (0,0,4), (2,2,4) and (2,2,4). The density of state (DOS) these sites were presented at-19 eV to-14 eV for lower valance band and-6 eV to 0 for upper valance band. Both (0,0,4) and (0,2,4) planes shows highest possibility of cation substitution since the energy substitution are the lowest (~40 KeV). (2,2,4) plane composed of O-O interaction in which would contribute to the oxygen vacancy.