Chemical fixation of carbon dioxide into value-added products is a promising idea. However, its conversion to valuable organic compounds requires highly efficient and safe catalytic system. In this work, the catalytic efficiency of the nontoxic organic base 1, 4‑Diazabicyclo Oct-4-ene (DBO) and its improved result after it has been cooperated with LiI salt have been studied. We gained more insight into the catalytic effects of DBO/LiI on the fixation of CO2 by means of density functional theory calculations using exchange–correlation functional B3LYP through basis sets of LANL2DZ for iodine and 6–31 + G(d,p) for non-iodine atoms. The calculations were carried out in both gas phase and in the presence of water as a solvent. Two reaction mechanisms were proposed and their respective energy was investigated to identify the favorable path for DBO/LiI system catalyzed reaction. Mechanism I is more favorable, in which the ring-opening of epoxide is the rate-limiting step which demands 32.20 kcal mol−1 Gibbs free energy of activation in the gas phase and 20.60 kcal mol-1in water. Lastly, this work validates that DBO in the presence of LiI displayed better catalytic activity for the title reaction and water is a good solvent for DBO/LiI catalyzed cycloaddition of CO2 with an epoxide.