Abstract: Calcium oxide (CaO) has been widely used as an adsorbent in the purification of heavy metals in coal-fired flue gas. However, the adsorption efficiency is limited and a further modification is needed. The cerium (Ce) modification can redistribute the surface electrons and enhance the chemical activity of CaO. Therefore, the Ce-CaO (100) periodic model was established to study the adsorption mechanism of mercury, selenium, and lead pollutants in the coal-fired flue gas. The results show that, except for the physical adsorption of Hg⁰ on the Ce-CaO (100) surface, the other heavy metal pollutants are chemically adsorbed on the surface. The Ce-site and O-site are the main active adsorption sites of heavy metal pollutants. Intense charge transfer and strong interaction are observed between adsorption molecules and Ce-CaO (100). Moreover, the adsorption capacity of Ce-doped CaO (100) surface for heavy metal pollutants has been improved, especially the significantly increased capture capacity on Se⁰, SeO₂ and HgCl₂.