NOVELTY - Star-shaped carbon dioxide fixation carrier comprises cyclodextrin as core, and PGED as a polymer arm.    USE - The carrier is useful in preparation of carbon dioxide separation membrane material (claimed), and purification of biogas.    ADVANTAGE - The carrier comprising arm has amino group promoting carbon dioxide into delivery vehicle, exhibits carbon dioxide selective permeability properties when utilized in membrane material, and has high penetration selectivity to carbon dioxide/methane system. The method transfer free radicals during polymerization reaction; has stable polymerization reaction, and easy regulation, and controllable conditions; produces product with star-shape having different number of arms, different arm lengths, different molecular weights, and narrow molecular weight distribution of carbon dioxide, and good storage stability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) preparing carrier, comprising (i) dissolving 0.1-0.2 pts. wt. cyclodextrin in 5-10 pts. wt. N,N- imethylformamide by placing in an ice bath, under anaerobic conditions, and adding 0.2-0.6 pts. wt. 2-bromo-2-methylpropionyl bromide and 0.4-0.6 pts. wt. triethylamine, reacting at 0-50 degrees C, adding diethyl ether until the product is precipitated into a solid shape, and washing with acetone, and taking out ether and acetone by placing in an oven under vacuum conditions, to obtain resulting product macroinitiators CD-Br, (ii) dissolving 0.2-0.5 pts. wt. CD-Br in 5-10 pts. wt. dimethylformamide at 0-50 degrees C, under anaerobic conditions, and adding 3-6 pts. wt. glycidyl methacrylate monomer, adding 0.082-0.15 pts. wt. ligand, and adding 0.033-0.1 pts. wt. copper bromide initiator, carrying out polymerization reaction for 1-8 hours, exposing the materials to air, inactivating the initiator system, and terminating the polymerization reaction, and adding methanol until the precipitate morphology becomes solid, and taking out methanol by placing in oven under vacuum conditions, to obtain linear stellate CD-poly (glycidyl methacrylate) polymer (PGMA), and (iii) dissolving 0.2-0.5 pts. wt. stellate CD-PGMA in 4-10 pts. wt. organic solvent at 70 degrees C under anaerobic conditions, and adding 2-4 pts. wt. ethylene diamine and 1-2 pts. wt. triethylamine, carrying out ring-opening reaction, adding ether until the product is precipitated as a solid shape, taking out ether by placing in oven under vacuum conditions, and dissolving the product in water, and adding water to the product in a ratio of 100-500 ml/g, and dissolving the product, and dialyzing by placing the material into a dialysis bag having molecular weight cutoff of 2500-4500 mw by adding deionized water for 12-24 hours, and carrying out freeze-drying of the product placed in dialysis bag until all moisture content is removed, and obtaining the product; and    (2) preparing carbon dioxide separation membrane material, comprising (a) dissolving 2-8 pts. wt. poly(vinyl alcohol) in 50-200 pts. wt. distilled water, heating at 90 degrees C until the materials gets dissolved, cooling the solution to 0-30 degrees C, adding 8-32 pts. wt. CD-PGED, and degassing under vacuum conditions, to obtain CD-PGED-PVA casting solution, (b) coating the surface of a base film with CD-PGED-PVA casting solution, where the base film horizontally fixed with polyethersulfone glass, and drying for 24-72 hours, and (c) drying aqueous emulsion of silicone rubber-coated CD-PGED-PVA composite film surface for 24-72 hours, to obtain the product.