Abstract: Herein quantum chemistry methods were used to discuss the microscopic mechanism in the arsenic/hydrogen/oxygen reaction system during combustion by Gaussian09 and GaussView at the theoretical level of B3LYP/6-311G (3df, 3pd). Configuration of the reactants, intermediates, transition states, and products of 13 elementary reactions were optimized and the authenticity of these reactions were verified by frequency and intrinsic reaction coordinates. Finally, the kinetic parameters were calculated through KiSThelP based on the classic transition state theory. This study focused on some of the most important reations in the arsenic/hydrogen/oxygen system, which makes sense to establish arsenic dynamic model during combustion.