The electronical properties of a kind of anti-ferromagnetic Co-based layered compound oxide Ca 2 Co 2 O 5 are investigated by the density functional theory method. The results show that there are five sub-bands for spin up and down electrons, and there are many energy bands near Fermi energy which show wider allocation. The spin up electrons forms semiconductor type band structure with indirect band gap of 0.0112 eV, nevertheless the spin down electrons forms the metallic band structure. The contribution of s state electrons to density of states is the least, that of p state electrons is in the middle, while d state electrons contribute the most. The electrons of the CaCoO sub-layer contribute to the system much more than that of the electrons of CoO sub-layer. The Ca electrons contribute to density of state far from Fermilevel, the Co electrons contribute to density of states near Fermi level, and the O electrons form bands near Fermi level as well as －19 eV. The Co d and O p electrons contribute to electronic properties of the anti-ferromagnetic Co-based layered oxide Ca 2 Co 2 O 5.