First-principles calculations have been performed to investigate the ground state electronic properties of BaFeO3 (BFO).Local spin density approximation (LSDA) plus U (LSDA+U) treatment modified the metallic behaviour to insulated one with a band gap of 4.12 eV.The spontaneous polarization was found to be 89.3#C/cm2 with Berry phase scheme in terms of the mode theory of polarization.Fe-3d eg were split into two singlet states (dz2 and dx2-y2 ),and Fe-3d t2g were split into one doublet states(dxz and duz) and one singlet states(dxy) after Fe and O displaced along thec axis.Meanwhile the occupation numbers of dz2,dxz,dyz and OT Pz (on the top of Fe) were increased at the expense of those in xy plane.Our results showed that it was the sensitivity of hybridization to ferroelectric distortions,not just the total change of hybridization,that produced the possibility of ferroelectricity.Moreover,the increasing occupation numbers of OT pz and Fe dz2 favoured the 180~ coupling between Fe-3d eg and Fe-3d t2g,leading to ferromagneticordering,which has been confirmed by the increase of magnetic moment by 0.13μB per formula unit in the polarized direction.Hence,the magnetization can be altered by the reversal of exteal electric field.