The depth profile of interface of Ta2O5/Ta sample has been investigated and a new model to explain the profile data based on the altered layer induced by bombardment of energetic ions during the sputtering has been proposed successfully. The experimental data can be fitted very well and the parameters characteristic of the ion mixing and pile up effect can also be obtained by this model. The samples were prepared by the method of anodic oxidation with a thickness of 500?. All the surface analyses were performed by scanning Auger microprobe model PHI-590 at room temperature. The following results have been obtained: In contradiction with the generally accepted point of view, the depth profile curve dose not exhibit the form of error function. The dominant factor for Auger signal during the interface analysis is the altered layer with a thickness of 30-50? rather than the electron mean free path λ. And the depth profile resolution of interface analysis is determined by compromise between the ion mixing and pile up effect.