Abstract: Density functional theory (DFT) calculations were performed to investigate the reaction mechanism and potential energy surface of the 1,2- and 1,4-addition reactions of silabenzene-Cr(CO)3 complex (R) with H2O. The influences of the number of H2O molecule, mesityl substituent at Si atom, and tetrahydrofuran as a solvent on the energy surface of the reactions were also explored. The obtained results indicated that R may react with monomer, dimer and trimer of H2O respectively. The dimer of H2O adds to R more readily kinetically than the corresponding monomer and trimer. The coordination of silabenzene to the tricarbonylmetal center of Cr(CO)3 had only a little influences on the kinetic properties of the addition reactions.However, it had a much unfavorable effects on the thermodynamic properties, especially for 1,4-addition. The complete regioselectivity for the addition of H2O to R was determined mainly by thermodynamic factor. Mesityl substituent with large volume had an adverse effect on the potential energy surface of 1,2- and 1,4-addition reactions. Tetrahydrofuran as a solvent had an unfavorable influence on the title reactions both thermodynamically and kinetically.