Abstract: The reaction for SiH3+O(3P) was studied by ab initio method. The geometries of the reactants， intermediates， transition states and products were optimized at MP2/6-311+G(d,p) level. The singlepoint calculations for all the stationary points were carried out at the QCISD(T) /6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major pathway is the SiH3+O(3P)→IM1→TS3→IM2→TS8→HOSi+H2. The other minor products include the HSiOH+H， H2SiO+H and HSiO+H2. Furthermore， the products HOSi， HSiO and HSiOH(cis) can undergo dissociation into the product SiO. In addition， the calculations provide a possible interpretation for disagreement about the mechanism of the reaction SiH4+O(3P). It suggests that the products HSiOH， H2SiO and SiO observed by Withnall and Andrews are produced from the secondary reaction SiH3+O(3P) and not from the reaction SiH4+O(3P).