This study employs grand canonical Monte Carlo (GCMC) simulations to investigate the impact of functional group modifications (CH , OH, NH , and OLi) on the adsorption performance of CH /N on Ni-MOF-74. The results revealed that functional group modifications significantly increased the adsorption capacity of Ni-MOF-74 for both CH and N . The packed methyl groups in CH -Ni-MOF-74 create an environment conducive to CH , leading to the highest CH adsorption capacity. The electrostatic potential distribution indicates that the strong electron-donating effect introduced by the alkali metal Li results in the highest electrostatic potential gradient in Li-O-Ni-MOF-74, leading to the strongest adsorption of N , this is unfavorable for CH /N separation. At 1500 kPa the selectivity order of adsorbents for mixed gases was as follows: CH -Ni-MOF-74 > NH -Ni-MOF-74 > OH-Ni-MOF-74 > Ni-MOF-74 > Li-O-Ni-MOF-74. This study highlights that CH -Ni-MOF-74 possesses optimal CH selectivity and adsorption performance. Given the current lack of research on functionalized MOF-74 for the separation of CH and N , the findings of this study will serve as a theoretical guide and provide references for the applications of CH adsorption and CH /N separation.