The development of practical porous materials for the selective capture of CO2 from flue gas and crude biogas is highly critical for both environment protection and energy safety. Here, a novel metal-organic framework (FJI-H29) has been prepared, which not only has excellent acid-base resistance but also possesses polar micropores (3.4-4.3 Å) that can match CO2 molecules well. FJI-H29 can selectively capture CO2 from N2 and CH4 with excellent separation efficiency and suitable adsorption enthalpy under ambient conditions. Breakthrough experiments further confirm its practicability for both CO2/N2 and CO2/CH4 separation. All of these confirm FJI-H29 is a practical CO2 adsorbent. Modeling calculations reveal that the confinement effect of micropores and the polar environment synergistically promotes the selective adsorption of CO2, which will provide a potential strategy for the synthesis of a practical metal-organic framework for CO2 capture.