Using the density-functional theory combined with the projector augmented wave method, we have investigated the electronic structure of Be-doping wurtzite ZnO. The band structure, total density of states and partial density of states of BexZn1-xO are presented and show that the valence band maximum (VBM) is determined by O 2p electrons and the conduction band minimum (CBM) is occupied by the hybrid Be 2s and Zn 4s electrons. The energies of CBM increase and the energies of VBM decrease with increasing Be-doping concentrations. Both effects lead to broadening of the band gap. Furthermore, it was found that Be-doping can cause compressive strain in the crystal structure, which also widens the band gap.