The electronic structures of high Tc superconductors YBa2Cu2ScO7, including two cases of Sc substituting Cul and Cu2 sites, are studied. Sc-Cu2 replacement has effects on electronic structure of Cu-O layers, which may possibly destroy the high temperature superconductivity. However, our calculations show that it is more likely for Sc to substitute Cul site. It is shown that the overlapping splitting between the major bonding partial wave of Sc and its remaining four 3d orbitals is as large as 4eV. Thus one can detect experimentally, by near infrared fluorescence, whether Sc substitute Y or Cu sites in Sc-Y-Ba-Cu-O materials.