In this study, a facile and scalable in situ growth method was used to synthesize ZIP-8@GO composites. The obtained ZIF-8@GO were blended with a CO2-philic, comb copolymer yielding a series of mixed matrix membranes (MMMs), which were evaluated for their performance in separation of CO2/N-2. The effect of reaction time for ZIF-8@GO composites on gas separation performance was systematically investigated. Pure and mixture gas permeation tests indicated that MMM with ZIF-8@GO by in situ growth for 6 h exhibited the largest improvement (CO2 permeability: 475 Barrer and CO2/N-2 selectivity: 58.2) compared with pure polymers, with the overall CO2/N-2 separation performance exceeding the 2008 polymer upper bound. Our strategy that the in situ growth of ZIF-8 on GO provides an effective way to design MMMs with well filler dispersion, structural features and separation performance.