Abstract Membrane separation is an energy‐saving technology for carbon capture. However, it is subjected to permeability‐selectivity trade‐off limitation. Although chemical functionalization is proposed to boost separation efficiency, controlling sorption–diffusion process remains extremely challenging. In this study, a facile, controllable, and versatile chemical vapor amination strategy is reported to simultaneously tune gas sorption and diffusion in polymer of intrinsic microporosity (PIM)‐based membranes for improving carbon capture performance. Through simple exposure in amine vapors under mild conditions, nucleophilic substitution of amines toward ether and halogen groups induce grafting, ring‐opening, terminal replacement, chain‐scission, and crosslinking of PIM‐1, thereby underpinning CO 2 ‐philicity and tailoring passageway. The prepared CO 2 ‐philic membranes exhibit substantially improved CO 2 /N 2 selectivity over 30.8, about 226% as that of original one, accompanied by high CO 2 permeability of 2590 Barrer, which can surpass the trade‐off upper bound of polymer membranes. Our results reveal that post‐synthesis amination is an effective route to obtain high‐performance membranes.