CO2 capture and storage technologies have been adopted to eliminate anthropogenic CO2 emission. Compared with other methods, adsorptive separation technology using excellent adsorbents has attracted extensive attention for its operational flexibility and energy-efficient characteristics. Herein, we present a copper-based metal-organic framework, MOF-11, exhibiting highly efficient CO2/N-2 (15:85, v/v) separation performance. There are two kinds of channels with different pore chemistries in the framework, in which dense Cu open metal sites (OMS) were found in channel I, while channel H had a narrower pore window size and was mainly decorated with -CH2 moieties from the organic ligands. At 298 K, the CO2 uptake value of MOF-11 was 4.63 mmol/g at 100 kPa and 2.92 mmol/g at 15 kPa, respectively, which was superior to many other reported MOF adsorbents. Molecular simulation indicated that CO2 dominantly occupied channel I due to the strong electrostatic interactions with the dense Cu OMS in channel I. In comparison, more N-2 molecules were adsorbed into channel II through multiple weak van der Waals interactions with -CH2 moieties. Such a pore system gives MOF-11 high CO2/N-2 selectivity (ca. 116 at 298 K). Moreover, the dynamic separation of CO2/N-2 mixture gases on MOF-11 was further investigated by cyclic breakthrough experiments.