XPS measurements have been carried out to study the difference in the electronic state between the pure 2212 single crystal and the Gd-doped 2212 single crystal in Bi-based system. Experimental results show that the suppression of superconductivity by Gd doping is caused by the hole filling in the O2p orbital. The problems, such as that about the ratio of the intensity of the satellite peaks to that of main peak (Is/Im) the physical property of Bi-O layer and the contribution to the density of state (DOS) at Er for the Bi-based 2212 phase have also been discussed.