Using density-functional calculations within the generalized gradient approximation （GGA）＋U framework, we investigate the structural, electronic, and magnetic properties of the ground states of SrFeOn（n=2 and 2.5）. The magnetism calculations show that the ground states of both SrFeO2 and SrFeO2.5 have G type antiferromagnetic ordering, with indirect band gaps of 0.89 and 0.79 eV, respectively. The electronic structure calculations demonstrate that Fe cations are in the high-spin state of （dz2）^2 （dxz ,dyz）^2 （dxy）^1（dx^2-y^2）^1（S=2）, unlike the previous prediction of （dxz ,dyz）^3（dxy）^1（dx^2）^1（dx^2-y^2）^1（S=2） for SrFeO2, and in the high-spin state of （dxy,dxz,dyz,dx^2-y^2 ,dz2）^5（S=5/2） for SrFeO2.5.
