Abstract: The electronic structure calculations including the Mulliken population analysis,band structure,density of states（DOS）,partial density of states（PDOS）and electron density difference on SrTiO_3-δwithδ=0 andδ=0.125 were performed by the first-principles calculation of plane wave ultrasoft pseudo-potential technology based on the density function theory（DFT）.The calculated results revealed that due to the oxygen（O）vacancy electron doping,the Fermi level moved into conduction bands （CBs）for SrTiO_3-δwithδ=0.125 and the system showed metallic behavior.There was a new defect level below the bottommost of CBs when one O vacancy was introduced.The 3d states of the two Ti atoms nearest to the vacancy made significant contribution to it.The electrons introduced by the O vacancy were largely localized on the two nearest Ti atoms.Furthermore,the formation energies of neutral O vacancy were calculated in three typical equilibrium conditions.