The effective separation of C₂H₂/CO₂ is important for the purification of acetylene. However, because of their highly similar physical properties, separating them efficiently is challenging. Due to the special physical and chemical properties of fluorine, fluorine-containing frameworks have potential applications in gas separation. Here, two isoreticular two-dimensional covalent organic frameworks with kgd topology, defined as TFT-COF and TMT-COF, were designed and constructed via the [6+3] imine condensation reaction. Experimental studies show that the IAST selectivity of a fluorine-functionalized TFT-COF for C₂H₂/CO₂ separation is 4.18, which is higher than that of the fluorine-free counterpart of 2.72, at 298 K and 1 bar. GCMC simulation indicates that the improved selectivity of the TFT-COF for C₂H₂/CO₂ separation arises from the strong electronegativity of fluorine groups and the resulting increased polarity of the pore surface, leading to enhanced C⋯H interactions between C₂H₂ and the skeleton.