To investigate the characteristics of CO2 and CH4 adsorption across various functional groups and to clarify their thermodynamic attributes, slit models of functional groups with different pore sizes and moisture contents were constructed using the Materials Studio software program. The analysis focused on the characteristics of CO2 and CH4 adsorption in six distinct models comprising different functional groups. The results showed that the adsorption activities of the six functional groups followed the order –CHO>–COOH>–OH>-O-CH3 > –CH3 > –CH2CH3. The average adsorption heat of the oxygen-containing functional groups exceeded that of the aliphatic groups for both the single- or two-component injections of CO2. As the moisture content increases, the maximum adsorption capacity of CH4 in the slit models with –CH2CH3, −O-CH3, –COOH, and –OH functional groups show a significant decreasing trend when injecting CH4 with two components. The absolute value of the adsorption energy of CO2 and CH4 decreases with increasing pore size. In the slit models with –CHO and –COOH functional groups, multiple peaks appear in the adsorption energy of CO2, indicating a greater number of adsorption sites. For the two-component injection of CO2 and CH4, the entropy of CO2 in each functional group was minimized at a pore size of 1 nm.