Abstract: Disclosed herein is a gas separation membrane for a DEM production process, including: a porous support having a carbon dioxide permeability of more than 300 GPU (GPU=1×10?6 cm3/cm2·sec·cmHg) and an inner diameter of 100˜1000 ?m; and a composite membrane provided on an inner or outer surface of the porous support and coated with a separating material having a permeation selectivity of carbon dioxide/hydrogen of 4 or more. The gas separation membrane is advantageous in that it can improve efficiency of the separation process by selectively separating and removing carbon dioxide from a gas mixture of carbon dioxide and hydrogen produced during a process of producing DME which is a next-generation clean fuel.