The　CO2　adsorption　on　CaO(001)　surface　at　different　coverages　from　1/9　monolayer　(ML)　to　1　ML　has　been　investigated　using　density　functional　theory　calculations.　With　the　analysis　of　the　most　stable　adsorption　structures　at　different　coverages,　the　mechanism　of　CaO　(001)　surface　carbonating　into　CaCO3　has　been　explored.　At　low　coverages　(＜=　1/3　ML),　CO2　molecule　prefers　sitting　in　parallel　pattern　on　the　CaO(001)　surface,　while　the　structure　of　the　CaO(001)　surface　remains　unchanged.　At　medium　coverage　(4/9　similar　to　2/3　ML),　the　repulsive　interactions　between　oxygen　atoms　of　CO2　become　stronger,　and　the　calcium　carbonation　structure　appears　on　the　CaO(001)　surface.　At　high　coverage　(＞=　7/9　ML),　the　structure　of　the　CaO(001)　surface　is　deeply　damaged,　and　a　few　CO2　molecules　have　penetrated　into　the　surface　and　bound　to　the　O　atom　of　the　second　layer　(sub-surface),　eventually　forming　the　layered　structure　of　CaCO3.　Additionally,　herein　has　discussed　the　simulation　of　HREELS　and　thermodynamical　stability　of　these　structures　at　different　coverages.