The Xα method is applied to study the spin-polarized electronic structures and atomic magnetic moments of clusters La8-xBaxCuO6 in the compound La2-yBayCuO4.This paper shows that Cu magnetic moment in La2CuO4 is 0.37μB, which is in better agreement with the experimental value(0.48±0.15μB). Ba substitution lowers the structure symmetry, removes molecular orbital degeneracy, and hence strengthens orbital hybridization and weakens quasi-two-dimensional feature, which enhance the coupling between Cu-O layer and the neighbormg layers and influence the charge transfer. These changes strongly affect the properties of carriers. Holes are introduced due to Ba substitution and they mainly enter into O sites, a few d-electronic holes enter into Cu sites, which causes important effects on the density of states, atomic magnetic moment and valence states of Cu and O in Cu-O layers. The results confirm that the holes are not always beneficial to the superconductivity. At the beginning the holes are beneficial to the superconductivity; they can decrease the superconductivity when more holes are introduced. This paper can explain that the transition temperature of high-temperature superconductive oxides changes with the variation of the doping level.