Using the hybrid Monte Carlo simulation code ACAT-DIFFUSE, we have investigated the two-component target sputtering and the associated stoichiometric changes near the surface, where we employed PdxPt1−xas a two-component alloy. The present ACAT-DIFFUSE code can estimate the slowing down process of energetic ions and the thermal process of moderated atoms. If the surface segregation is ignored, the simulation showed that the Pd signal of Auger electron spectroscopy (AES) should be larger than that of low energy ion scattering spectroscopy (ISS). If the segregation energy and the associated effective diffusion constant are properly selected, the simulated ISS values and the AES values of the Pd concentration are in good agreement with the experimental ISS and AES values.