Abstract: In order to explore the adsorption mechanism of Mn(Ⅱ) on illite surfaces, the density functional theory (DFT) was used to simulate the adsorption of Mn(Ⅱ) on the (001) and (010) surfaces. The active site, adsorption configuration, charge and state density were studied, and the following conclusions were obtained. On the (001) surface, Mn(Ⅱ) was adsorbed preferentially on the hole of silicon oxygen ring and formed a covalent bond with the active oxygen O_S1, with an adsorption energy of -262.55 kJ/mol. On the (010) surface, Mn(Ⅱ) formed 1 to 3 covalent bonds with O_S from hydroxyl groups, and the adsorption energy increased with the increase of covalent bonds. The most stable adsorption configuration was Mn(Ⅱ) adsorbed on the holes between three ≡Al—OH groups, and the adsorption energy was -533.62 kJ/mol. There were covalent bond interactions and electrostatic interactions between Mn(Ⅱ) and the (001) and (010) surfaces. The adsorption energy of Mn(Ⅱ) on (001) surface was less than that on the (010) surface. The adsorption of Mn(Ⅱ) on the (001) surface was mainly electrostatic interaction and that on the (010) surface was mainly covalent interaction. The formation of the surface covalent bond between Mn(Ⅱ) and illite was mainly due to the interaction between the 4s orbital of Mn and the 2p orbital of O_S. The results can provide a theoretical basis for the development of clay adsorption materials or the purification of contaminated soil.