The metal materials with high work function should be used as the back electrode of CdTe solar cells. In the present paper, the back contact performances of CdTe solar cells with Au film and Ni film, respectively, were studied by X-ray photoelectron spectrum (XPS). After exfoliating the back electrode film, it was found that Au on the surface of ZnTe/ZnTe:Cu complex back contact layer is in the form of Au atoms and the concentration and depth of Ni diffusing into the ZnTe/ZnTe:Cu back contact layer are higher than that of Au. What's more, some Ni changes into Ni(x)+ ion which leads to rich Te ions in ZnTe/ZnTe:Cu back contact layer. So the diffusing concentration is increased, which makes the characters of CdTe improved. In the samples, the displacement of either Te or Zn peak position changes little, which indicates that both Te and Zn do not change in the modality.