Abstract: In this article,the adsorption mechanism and microstructures of the methane in slit-like clay mineral pore (montmorillonite,illite,chlorite and kaolinte) have been investigated by using Grand Canonical Monte Carlo simula- tions and molecular dynamics simulation,and the influence of different pore sizes,different pressures on the methane adsorption on clay minerals have been discussed. The results show that the isosteric heat of methane decreased with the increase of pore size,which was less than 42 kJ / mol,suggesting that the adsorption of methane on clay minerals was physical adsorption. The methane molecules affected by the potential energy of pore walls gathered near pore walls to form adsorption phase. However,the area far away from hole walls were not affected by the potential energy of pore walls and methane molecules as free phase were dispersed in pores. The adsorption capacity of methane increased with the increase of pore size in micropore,whereas the adsorption capacity of methane decreased with the increase of pore size in mesopore. The proportion of the adsorbed gas amount of methane molecules in pores decreased as pressure or pore size increases. From the microcosmic point of view,the methane adsorption capacity on clay minerals was approximately same in the same pore size,whereas from the macroscopic point of view,the methane adsorption capacity on clay minerals had a bigger difference,illustrating that the methane adsorption capacity on the different types of clay minerals was mainly affected by the factor of specific surface area. The proportion of the adsorbed gas amount of meth- ane molecules in pores showed a decreasing trend as pressure or pore size increases.