The invention discloses a preparing method of compound amino acid, and relates to the technical field of preparation methods of amino acid. The preparing method comprises the following steps of manufacturing of a sizing agent, wherein leucine, valine and isoleucine are mixed, afterwards, leucine, valine and isoleucine are poured into water, soybean meal, black rice powder and barley meal are addedafter leucine, valine and isoleucine are sufficiently dissolved, and after leucine, valine and isoleucine are emulsified into the sizing agent, a spray dryer is utilized for drying to obtain coarse powder; grinding, wherein the coarse powder is poured into a grinder and ground for 10 min, and then a40-60-mesh screen is utilized for filtering; pelletizing, wherein powder is poured into a pressingmold and pressed into amino acid particles, and then the amino acid particles are soaked in gelatin and fished out for use after 5 s; wrapping, wherein Chinese yam, potatoes and raisin are aired and afterwards ground into wrapping powder particles, the wrapping powder particles are laid on a plane after being uniformly mixed, and the amino acid particles are placed on a drying rack for airing after rolling across the surfaces of the wrapping powder particles; packaging. The preparing method of the compound amino acid has the advantages that nutritional ingredients are diversified; meanwhile, the compound amino acid is good in mouthfeel, a user has good satiety after eating the compound amino acid, the digestion time is short, and the compound amino acid has the capability of improving thecomplexion.