Siwafers annealed by CW-CO2 laser have been studied using Nomarski technique, electron absorption image, IR spectrum, AES and ESCA, with particular emphasis on the study of in-depth oxygen contamination. Electron absorption image shows that the effect of CW-CO2 laser annealing is not very uniform in our case. And it has also shown that CW-CO2 laser annealing in air would decrease the carbon contamination on the Si surface, but produce oxygen contamination. This oxygen contamination consists of two parts: SiOx on the surface and free oxygen atom underneath, its thickness is less than～250?.