Niobate materials, such as LiNbO₃, KNbO₃, LnNbO₄ (Ln=Pr, La, Ga, Y), etc. have attracted wide attention due to their excellent photosensitivity. However, the transition metal niobate is rarely studied, and the relationship between its photoelectric properties and vacancy defects has not been thoroughly explored. Here, the effect of vacancy defect on electro-optical characteristics of ZnNb₂O₆ system was studied based on first-principles of density function theory. Its geometric structure, electronic structure, and optical spectrum clearly revealed the effect of electro- negativity and geometric position of atoms on the structure and electronic energy level. At the center of the octahedron, atoms, such as Zn and Nb, contributed similarly to the energy band, and had relatively fixed positions on the valance band when they formed vacancy defects. However, Nb atoms with larger electro-negativity generated larger lattice distortions, more obvious negative shifts of the conduction band, and red shifts of the absorption edge upon the formation of vacancy defects, which are conducive to improving electro-optical characteristics. Atom O at the vertices of the octahedron generated smaller lattice distortions when vacancy defects formed. However, negative shifts occurred at the conduction and valance bands, and impurity energy levels emerged on the Fermi surface, which induced the formation of “capture traps” on the charge carriers. This in turn exerted a larger influence on the redistribution of charge, resulting in a blue shift of the system in whole, and an all-round enhancement of optical spectrum intensity.