In the paper，electronic structure and optical properties of Zn1-xBexO are calculated by CASTEP program based on density functional theory and plane-wave pseudopotential method. The band gap increases in the range from 0.963 eV to 7.293 eV when Be content changes from 0 to 1. The lattice strain and band repulsion affecting band gap is investigated. The variation of the band gap is dominated by a/b-axis strain for x=0.125，0.25，0.375，0.5，0.625 and 0.75. The variation of the band gap is dominated by c-axis strain for x=0.875 and 1. In the paper，p-d and Γ1v-Γ1c repulsion are used to investigate the top of valence band and the bottom of conduction band，respectively. In addition，we also investigate the imaginary part of the dielectric function，ε2 of Zn1-xBexO.