CO2 capture from natural gas and N2-rich flue gas is essential for improving the utilization of natural resource gases reducing CO2 emission, thereby alleviating the greenhouse effect. However, achieving effective Adsorptive separation of CO2 from CH4, N2, and O2 based on molecular sieving is still challenging and rarely reported, but selectively capturing CO2 places high desires on maximizing separation efficiency. Here, we report a zinc-aminotriazole ultramicroporous metal–organic framework (ZnATZoxH2O), constructed from zinc carbonate, 3-amino-1,2,4-triazole (ATZ), and oxalic acid with water as the only solvent. ZnATZoxH2O features NH2-functionalized and pore channels around 3.6 Å, which preferentially adsorb CO2. This material exhibits high CO2 uptake of 61.9 cm3 g−1 at 298 K and 1 bar and significantly high IAST selectivity for CO2/N2 (>103) and CO2/CH4 (>105) and CO2/O2 (>104). Theoretical GCMC simulations reveal that negatively charged amino groups decorated on the pore channel surface and carboxylic acid in the pore environment enhance the binding affinity over CO2 through electrostatic interactions for preferential capture of CO2. Single-component adsorption experiments and dynamic breakthrough experiments mutually validated the superior separation performance of this material and dynamic column breakthrough tests to produce high dynamic CO2 separation productivity of 2.017 mmol g−1 and 3.4 mmol g−1 for CO2/N2 (15/85), CO2/CH4 (50/50), and 2.26mmol g−1 CO2/N2/O2 (15/80/5). Non-hazardous water as a synthetic solvent to assemble highly stable and efficient CO2-selective materials makes it promising for practical industrial applications.