Abstract: The generalized gradient approximation (GGA)and PW91 functional of the first principle were used to study the effect of oxygen as cocatalyst in Rochow reaction. The results show that there exists three polarized bonds of Si－Cu, Cu－O and Si－O between the raw material silicon and oxygen-containing catalyst. For the polarization of C－Cl bond in CH₃Cl, the Si－Cu bond is the main catalysis center. In the catalyst clusters with less than 4 Cu atoms, O atoms can promote significantly the electron cloud transfer of Si－Cu bond to O, and improve the catalytic effect of Si－Cu bond. In the catalyst clusters with more than 4 copper atoms, the O atom is far away from the Si－Cu bond, and its catalytic effect can be ignored.