TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In preparing composite film for separating mixed gas of carbon dioxide and firedamp, the porous carrier is in shape of a sheet, tube or hollow fiber or is made of silicon sheet or stainless steel or ceramics; the aperture of the porous carrier is 3 microns to 0.05 microns. The porous carrier is pre-treated through burnishing, ultrasonically vibrating and high temperature baking. The average grain size of the SAPO-34 molecular sieve is 0.5-0.02 microns. The organic precursor is poly-furfuryl alcohol, polyimide, phenolic resin or polyacrylonitrile; and the solvent is N,N-dimethylacetamide, ethanol or acetone. The organic precursor solution containing SAPO-34 molecular sieve is supposed to be fiercely mechanically stirred and ultrasonically vibrated so as to fully disperse the SAPO-34 organic solution; the content of the SAPO-34 molecular sieve in the film preparing mixed liquid is 0.5-30wt%; the film coating method is one of dipping pulling method, vacuum pulling method, spraying painting method, thermal coating method and ultrasonic sediment method; the film is coated for 1 to 6 times; the porous carrier is supposed to be dried for 2 to 72 hours after being coated; after that, the SAPO-34/organic matter composite film is carbonized in vacuum or inert gas at temperature of 400 to 1000 degrees C; the heating speed and the cooling speed is between 0.1-10 degrees C per minute. The SAPO-34/C composite film has perfect separation performance in separating mixture of CO2/CH4; when the pressure on the two sides of the film is reduced to 0.1 MPa at room temperature and the mol ratio of H2/CH4 is 1:1, the separation coefficient of the H2 to the CH4 is as high as 89; at this moment, the permeability of the H2 reaches 7.1X10-8 mol/Pa/m2/second. The SAPO-34/C composite film has perfect separation performance in separating mixture of CO2/CH4; when the pressure on the two sides of the film is reduced to 0.1 MPa at room temperature and the mol ratio of H2/CH4 is 1:1, the separation coefficient of the H2 to the CH4 is as high as 89; at this moment, the permeability of the H2 reaches 9.2X10-8mol/Pa/m2/second.