We can see that the upper position of the valence band has major influence after doping. Furthermore, the O-p states and s-DOS on either side the Fermi stage tend to be sharpen by the O atom after Ag doping in present lattice. Fig 3 (a) shows the PDOS of pure SrTiO3 and Ag-doped SrTiO3 we observed that the value of Ag-doped SrTiO3 is maximum as compared to pure SrTiO3. The elemental PDOS was plotted to compare the pure and doped systems Fig 3 (b & e) that exhibit major differences in valance and conduction band states before doping and after doping. Fig 3 (c) shows the PDOS of pure and Ag-doped Ti, we observed that value of Ag-doped Ti is greater as compare to pure Ti. Fig 3 (f) shows the TDOS and for pure and Ag-doped SrTiO3, we see that the top at the valence band is in the limit of 0 to 5 electron Volt generates deep effect, according to the TDOS, due to recently emerging Ag-d states. By appearance the Ag- d states at the upper point of the valence band at point G could explained an upper change in the valance band. As a result, we claimed that Ag doping in SrTiO3 has two significant consequences. The first shows the reduction in band gap reasoned of inclusion of Ag in SrTiO3. Second, we see alter in structure of the band gap after doping from indirect to direct. As a result, Ag doped SrTiO3 would be much effective for optical devices [17,18].