Since the inception of membrane-based CO2 separation technology in the late 1970s, a large number of material studies have been performed to improve the material properties of membrane materials and tremendous progress has been made with regard to CO2 separation to increase the trade-off between permeability and selectivity, known as the "Robeson upper bound." In membrane science, material properties and membrane properties are related but completely different, especially in thin-film composite (TFC) membranes. Compared to the large number of material studies, few studies have been performed on membrane properties, and very few membranes have been successfully commercialized because an extremely thin selective layer is required in CO2/N-2 separation membranes for high CO2 permeance; however, defects are easily generated, deteriorating gas transport properties on a large-scale. In this study, we theoretically analyzed the effect of defects on the gas transport properties of a TFC membrane and introduced a method to control defects during the preparation of large-scale membranes. This work will provide a facile and practical approach to preparing TFC membranes and will be helpful toward extending material studies to real membrane demonstrations.