NOVELTY - Preparing silane gas comprises: (a) placing 100-350 meshes of metallurgical silicon powder into mixed acid of hydrofluoric acid and nitric acid, and etching for 0.5-2 minutes under ultrasonic action, and washing the etched silicon powder into neutrality, and drying; (b) adding etched silicon powder into a copper catalyst pre-precipitation solution, extracting vacuum, and adding precipitation initiator; and (c) placing the organic inert solvent with high boiling point and silicon-copper contact mass into a reaction agitating kettle, and heating.    USE - The process is useful for preparing silane gas (claimed) that is used for producing amorphous silicon film solar battery, and light emitting diode and liquid crystal display industries.    ADVANTAGE - In utilizing the process, the selectivity of the prepared trialkoxyl silane reaches 95%; where the conversion rate is 90%; the decomposition rate of trialkoxyl silane is 99.8%; the silane yield is 90-93%; and the purity is 99%.    DETAILED DESCRIPTION - Preparing silane gas comprises: (a) placing 100-350 meshes of metallurgical silicon powder into mixed acid of hydrofluoric acid and nitric acid, and etching for 0.5-2 minutes under ultrasonic action, and washing the etched silicon powder into neutrality, and drying; where the mol ratio of hydrofluoric acid to nitric acid is 1:10 to 10:1; (b) adding etched silicon powder into a copper catalyst pre-precipitation solution, extracting vacuum, and adding precipitation initiator into mixed solution of silicon powder and copper catalyst pre-precipitation solution under ultrasonic action until there is no settlement, and filtering, vacuum drying to obtain silicon powder compound body coated by copper catalyst, and pre-treating for 1-3 hours at 200-560 degrees C under hydrogen or nitrogen atmosphere, or pre-treating for 1-3 minutes under 2450 MHz of microwave, obtaining silicon-copper contact mass with many active points and even active points; where the copper catalyst pre-precipitation solution is cuprous chloride pre-precipitation solution or copper hydroxide pre-precipitation solution; and the mass ratio of etched silicon powder to copper-based catalyst pre-precipitation solution is 1:5-10; and (c) placing the organic inert solvent with high boiling point and silicon-copper contact mass into a reaction agitating kettle, and heating at 200-260 degrees C, and adding fluoride corrosion-inhibiting etcher into the reaction kettle, and infusing the alcohol decomposing inhibitor and alcohol gasification gas obtained after dehydrating the ethyl n-silicate into the reaction agitating kettle, reacting for 5 hours, and obtaining trialkoxyl silane; where the mass ratio of organic inert solvent with high boiling point to silicon-copper contact mass is 2-10:1; the mol ratio of silicon-copper contact mass to infused alcohol in the whole reaction process is 1:5-8; the alcohol has 1-4 carbon atoms; the dosage of the fluoride corrosion-inhibiting etcher is 1-10% of silicon-copper contact mass; the method for preparing the fluoride corrosion-inhibiting etcher comprises adding molecular sieve into fluoride solution having a mass concentration of 5-30%, and decompressing and sucking gas, filling fluoride solution in bore channel of the molecular sieve, and drying to obtain fluoride corrosion-inhibiting etcher; where the mass ratio of molecular sieve to fluoride aqueous solution is 1:10-17; the mass ratio of fluoride to molecular sieve in the corrosion-inhibiting etcher is 0.5-5.1:1; the alcohol decomposing inhibitor is alkaline metal sulfide, dimethyl sulfide, carbonyl sulfide, methanthiol, carbon disulfide, dimethyl disulfide, thiophene, chloromethane, or chloroethane; the mol ratio of infusion amount of alcohol decomposing inhibitor to alcohol is 0.01-1 mmol: 1 mol; and the catalysis corrosion inhibitor is prepared by dissolving catalyst for disproportionating the trialkoxyl silane into organic solvent, preparing catalyst solution having a mass concentration of 5-10%, and immersing expansion graphite into catalyst solution, extracting vacuum to infiltrate the catalyst solution in gaps of the expansion graphite, when there is no bubble on surface of the expansion graphite, vacuum drying the expansion graphite filled with catalyst solution at 50-70 degrees C; where the catalyst is the first main group oxide, the first main group hydroxide, the first main group low-grade fatty alcohol salt, the second main group oxide, the second main Group hydroxide, the second main Group low-grade fatty alcohol salt, iron, iron oxide, cobalt, cobalt oxide, nickel, nickel hydroxide, manganese, manganese oxide, and platinum, or their mixture; the ratio expansion graphite to catalyst solution is 1:5-10; the ratio of catalyst to expansion graphite in the catalysis corrosion inhibitor is 0.25-1:1; and placing the catalysis corrosion inhibitor in dry reaction kettle, sealing the reaction kettle, and after blowing the sealed reaction kettle for 20-35 minutes with high-pure nitrogen, and blowing the sealing reaction kettle for 20-30 minutes with hydrogen, infusing the trialkoxyl silane into the reaction kettle, and starting up constant temperature to agitate; where the agitating speed is 250-400 turns/minute; and controlling pressure intensity in reaction kettle to be negative 0.1 MPa to 1.2 MPa, and heating at 35-100 degrees C for 15-30 minutes, reacting for 0.2-1 hours, and obtaining silane gas; where the mass of the catalysis corrosion inhibitor is 20-50% of mass of the trialkoxyl silane.