The adsorption and dissociation of CO and CO₂ molecules on UO₂ (111) slab were investigated by the first-principles calculations based on density functional theory with the addition of Hubbard term for calculation correction. Different static and dynamic adsorption mechanisms under different configurations were analyzed, and the adsorption sites included top, hollow, and bridge sites. In the static calculations, the variation of adsorption parameters, such as adsorption configuration, adsorption energy, and charge transfer, during adsorption process was investigated. ab-initio molecular dynamics (AIMD) was employed to study the dissociation process of CO₂ molecules and the changes in charge density difference. Results show that the adsorption of CO molecules can be categorized into two types: (1) stable adsorption, including chemical and physical adsorptions; (2) unstable adsorption. The adsorption types of CO₂ on UO₂ (111) slab only include the chemical adsorption of stable adsorption and unstable adsorption. No physical adsorption exists. The optimal configuration for the adsorption of both CO and CO₂ molecules is short-bridge vertical (B-short-Ver) adsorption. Additionally, at 0 K, the CO₂ molecules at the configurations related to B-short-Ver adsorption and long-bridge vertical adsorption on UO₂ (111) slab spontaneously dissociate after adsorption. AIMD simulation results show that both configurations dissociate at 300 K.