Recently, the composite materials consisting of ionic liquids (ILs) and metal-organic frameworks (MOFs) have attracted a great of attention due to their fantastic properties. Many theoretical studies have been performed towards its special structures and applications. Yet, the mechanism for the diffusion of ILs inside MOFs channels still remain unclear. Here, the DFT calculations together with frontier orbital analysis, natural charge analysis, and energy decomposition analysis were performed to investigate the diffusion behavior of a typical IL, [C4mim][PF6], into the ZIF-8 SOD cage. The potential energy surface (PES) profiles indicate that it is quite difficult for the cation [C4min]+ to diffuse into the cage of ZIF-8 through the pristine pores because of its large imidazole steric hindrance. Moreover, the PES reveals that a success diffusion could be obtained by the thermal contributions, by which the pore size is enlarged through the swing effects at a higher temperature. Subsequently, electronic structure analyses reveal that the main interactions between [PF6]-or [C4mim]+ and ZIF-8 is the steric repulsion interactions. Finally, the effects of amounts of [C4mim][PF6]on the ZIF-8 were investigated, and the results show that two pairs of [C4mim][PF6] per SOD cage is more reasonable in terms of interaction energies and structural changes.