NOVELTY - Preparation of silico-aluminophosphate (SAPO)-34 molecular sieve membrane for selectively separating methane gas comprises (a) synthesizing inoculating crystal; (b) preparing inoculating crystal base membrane; and (c) synthesizing SAPO-34 molecular sieve membrane.    USE - The process is useful for preparing SAPO-34 molecular sieve membrane for selectively separating methane gas (claimed).    ADVANTAGE - The SAPO-34 molecular sieve membrane synthesized by adopting the method can be suitable for each kind of porous carrier with smooth surface; it not only has high repetitiveness and good orientation, but also has good separating property and super high gas penetrance, and is suitable for using in industry.    DETAILED DESCRIPTION - Preparation of SAPO-34 molecular sieve membrane for selectively separating methane gas comprises (a) synthesizing inoculating crystal: the mixture ratio of inoculating crystal reaction solution is: 1mol aluminum oxide (Al2O3): 0.7-1.5mol phosphoric acid (H3PO4):0.3mol silicon dioxide (SiO2):1-1.5mol tetraethylammonium hydroxide (TEAOH):50-100mol water (H2O), adding phosphoric acid, tetraethyl amine oxide and silicon solution after sufficiently hydrolyzing the aluminum isopropoxide, adjusting the solution pH value to 5-6, crystallizing for 1-3 days in the water at 150-180 degrees C, rinsing and airing the product to obtain inoculating crystal powder; (b) preparing inoculating crystal base membrane: preparing the inoculating crystal powder in (a) to 1-20 g/L suspension, dropping inoculating crystal suspension on the surface of carrier after cleaning and drying it, heating up to evaporate the solution for drying to obtain inoculating crystal base membrane on the carrier; (c) synthesizing SAPO-34 molecular sieve membrane: the mixture ratio of molecular sieve synthetic mother solution is 1mol Al2O3:0.7-1.5mol H3PO4:0.3mol SiO2:1-1.5mol TEAOH:100-300mol H2O, adding phosphoric acid, tetraethyl amine oxide and silicon solution after sufficiently hydrolyzing the aluminum isopropoxide; putting the inoculating crystal base membrane of (b) in the reaction kettle, adding in molecular sieve synthetic mother solution, hotly crystallizing for 3-20 days in the water at 150-180 degrees C, cleaning and airing after putting out, activating at 400-600 degrees C to remove template to prepare SAPO-34 molecular sieve membrane on the carrier.