High-performance mixed matrix membranes (MMMs) were developed to assist in controlling global warming by capturing carbon dioxide (CO2) from moist flue gas. However, the separation performance of MMMs has always been limited by gas permeability and long-term operating stability under humid conditions. ZIF-302 is a novel chabazite (CHA) topology structure with hydrophobic ligand. Herein, uniform ZIF-302 nanocrystals were doped into the P84 polymer matrix to synthesize different content of defect-free ZIF-302/P84 MMMs for CO2/N2 separation. A significant combination of gas permeability and separation factors was found in MMMs with a ZIF-302 packing load of 30 wt%. The gas permeability of CO2 and the separation factor of CO2/N2 were significantly increased to 5.2 Barrers and 46, respectively, which breaks the trade-off between permeability and selectivity of the polymer membrane. In addition, the long-term operation stability showed that the separation performance of ZIF-302/P84 MMMs for CO2/N2 was maintained more than 30 h at 3 bar and 60 oC. The main characteristics of the MMMs prepared in this paper include the combination of favorable structural stability under humid conditions and unaffected CO2/N2 gas separation performance.