Abstract: The geometries of Li_xNi_0.5Mn_0.5O₂ was optimized by density functional theory (DFT) plane-wave ultrasoft-pseudopotential method, and then the corresponding electronic structure and average intercalation-Li voltage were calculated. The results indicate that when x=1, the d orbital electron of Ni, Mn and part of O2p near the fermi surface are electronic contributors; O2p and Ni(Mn) 3d orbials form strong covalent bonds. The bond length of Ni-O is similar to that of Mn-O, which inhibits the distorting of M-O octahedron. LiNi_0.5Mn_0.5O₂ is not only a good electric conductor but also owns stable structure. Li exists in layer material mainly in the state of Li⁺, which is conducive to deintercalation and diffusion. The electrical conductivity gradually becomes poor with the deintercalation of Li-ion and the increase of band gap.