NOVELTY - A mixed matrix membrane of double-layer hollow fiber comprises a mechanical supporting inner layer of organic polymer. The wall thickness of the inner layer is 40-250 mu m. The mixed matrix membrane is a selective separating outer layer with a wall thickness of 0.1-10 mu m. The dispersed phase of the mixed matrix membrane is a molecular sieve having a caliber of gas molecule size range.    USE - A mixed matrix membrane of double-layer hollow fiber used in the separation of oxygen and nitrogen in air, separation of acid gas (carbon dioxide and hydrogen sulfide) in natural gas and methane, separation of carbon dioxide and nitrogen in the burning waste gas, separation of hydrogen, carbon monoxide, and carbon dioxide in water gas, and separation of hydrogen in synthetic ammonia.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for preparing a mixed matrix membrane of double-layer hollow fiber comprising preparing a casting solution of mechanical supporting inner layer by stirring and dissolving 10-30% organic polymer, 2-20% caliber adjusting agent, and 50-88% solvent at 25-80 degrees C. The casting solution of mixed matrix membrane of selective separating outer layer is prepared by stirring and dissolving 20-39% organic polymer, 2-20% caliber adjusting agent, 2-29% molecular sieve, and 30-76% solvent at 25-80 degrees C. The core solution is prepared by stirring and dissolving solvent and water at 25-80 degrees C. The solvent is 50-95% of water solution. The core solution and casting solution are injected to a core solution passage of three-passage spinning nozzle and an inner and outer casting solution passage by a gear pump, and sprayed from the spinning nozzle outlet for forming a tubular solution membrane. After the solution membrane passes through the air gap of 0-20 cm, it enters the coagulating bath and is twisted on the wire winding wheel. The phase change is solidified into a mixed matrix membrane of double-layer hollow fiber. The formed mixed matrix membrane of double-layer hollow fiber is soaked in the water for 3 days, and arranged in methyl alcohol and hexane for 1-2 hours, and dried in the air. The mixed matrix membrane is arranged in a high-temperature vacuum furnace for warming to post heat treatment temperature from room temperature under the vacuum state to maintain 0.5-3 hours at the temperature. The post heat treatment temperature is decided by the glass state temperature of organic polymer. The glass state temperature of organic polymer adds and subtracts 20-50 degrees C, it is cooled naturally to the room temperature.    DESCRIPTION OF DRAWING(S) - The drawing is a sectional view of a mixed matrix membrane.