NOVELTY - A hybrid film has a polyimide film as substrate having thickness of 80-110 mu m, and hydrogel microspheres having particle size of 250-300 nm filled in the matrix of the substrate. The mass ratio of polyimide and hydrogel microspheres is 1:0.05-0.5. The hydrogel is obtained by carrying out polymerization of N-isopropyl acrylamide and N,N-methylenebisacrylamide.    USE - Hybrid film is used for separating carbon dioxide-and-methane mixture (claimed).    ADVANTAGE - The hybrid film is efficiently manufactured by simple method, and separates carbon dioxide-and-methane mixture efficiently under low wet test condition and osmotic coefficient of 270 barrer. The polymer matrix in the hybrid film has excellent compatibility. The hydrogel microspheres increase water absorption rate of the hybrid film.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) preparation of hybrid film. Isopropyl acrylamide monomer and N,N-methylene-bisacrylamide are added to a four-necked flask in the mass ratio of 14:9, and deionized water is added to form N-isopropylacrylamide solution having concentration of 0.14 g/mL. The solution is mechanically stirred, heated at 90 degrees C for 30 minutes, and aqueous solution of potassium persulfate initiator having concentration of 0.1-0.15 is added, such that the ratio of N-isopropylacrylamide and potassium persulfate initiator is 7:5. The resultant product is reacted at 90 degrees C for 6 hours, repeatedly washed by centrifugation, and dried to obtain hydrogel microspheres having particle size of 250-300 nm. Polyimide resin is added to N,N-dimethyl formamide solution having concentration of 4-10%, stirred at room temperature for 8-16 hours and completely dissolved to obtain polyimide resin solution. The obtained polyimide resin solution is mixed with hydrogel microspheres, stirred at room temperature, and the obtained casting solution is cast for 8-16 hours at 50 degrees C in an oven and dried for 12 hours to obtain hybrid film; and    (2) application of hybrid film for separating carbon dioxide-and-methane mixture with the selectivity of 35-65.