We study the electronic and magnetic properties of an oxygen-deficient perovskite Ca2Mn2 O5 based on the first principle calculations.The calculations show that the ground state of Ca2Mn2O5 is a D-type anti-ferromagnetic structure with the anti-ferromagnetic spin coupling along the c-direction.The corresponding electronic structure of the D-type state is investigated,and the results display that Ca2Mn2O5 is an insulator with an indirect energy gap of ～2.08 e V.By the partial density-of-state analysis,the valence band maximum is mainly contributed to by the O-2p orbitals and the conduction band minimum is contributed to by the O-2p and Mn-3d orbitals.Due to the Coulomb repulsion interaction between electrons,the density of state of Mn-3d is pulled to-6--4.5 eV.