Based on data of neutron diffraction measurements, the oxidation states in Y1-xPrxBa2Cu3O7-δ system are determined by bond valence sums (BVS) calculation. It is found that a close correlation between the BVS value of Cu(2) and superconducting critical temperature (Tc) exists. We believe that the increase of Pr content leads to the variation of charge distribution when the content of oxygen remains almost constant. At the same time ,the BVS value of Cu(l) and Cu(2) decreases,while that of Y(Pr) increases,and the holes in CuO2 plane are partly localized in Pr-O bond. The quenching of superconductivity by Pr ions is mainly attributed to this localization of the holes in CuO2 plane by Pr ions.