Metal-organic framework (MOF) is one of the porous materials that can be used in various fields of science and industry. In order to improve its performance, a MOF-based composite material, such as MOF - graphene oxide (GO) composite has been introduced. First synthesized in 2009, MOF-GO composite has been regarded as a promising material for gas separation and storage due to its enhanced adsorption properties. Although there have been some studies about MOF-GO composite, a detailed understanding in molecular-level is still unknown. In this research, computer modelling and molecular simulation are used for the first time to figure out the MOF-5/GO structure and its properties. It is concluded that, the enhanced properties of MOF-5/GO in gas adsorption is related to MOF-GO interfacial region. In order to maximize its enhancement, a structure that contains large proportional volume of MOF-GO interfacial region is suggested. It is also recommended to apply this material to separate small and large gas molecules, such as natural gas purification.