<p>Mixed-matrix membranes that combine the merits of polymer and filler materials offer high potential for molecular separations, but precisely engineering the filler phase structure to give full play to the role of filler materials remains challenging. Herein, we explore a reverse-filling approach to fabricate mixed-matrix membranes with continuous and vertically penetrating covalent organic framework channels for CO₂ separation. Covalent organic framework nanosheets as building blocks are pre-assembled into a robust and vertically oriented covalent organic framework scaffold via ice templating method, with the subsequent polyimide filling into the scaffold. The scaffold inherits the intrinsic CO₂-philic pore structure of nanosheets, which serves as fast and selective CO₂ transport channels in the membrane. The resulting membrane exhibits high CO₂ permeability of 972 Barrer and CO₂/CH₄ selectivity of 58, along with long-term stability and scale-up capability. This approach may stimulate the thinking about how to design advanced mixed-matrix membranes.</p>