The invention discloses yak, cow and ewe three-in-one composite infant formula milk powder and a preparation method thereof. The yak, cow and ewe three-in-one composite infant formula milk powder is prepared from fresh yak milk, fresh cow milk, fresh ewe milk, vegetable oil, dehydrated butter, lactose, decavitamin, mineral elements, taurine, linoleic acid, eicosatetraenoic acid, docosahexaenoic acid, compound trace elements, choline, prebiotics, casein phosphopeptides, nucleotide, lactoferrin, whey protein powder, 1,3-olein-2-palmitin, inositol, L-carnitine and demineralized whey powder. The production method includes the steps of milk collecting, storing, material blending, preheating, homogenizing, sterilizing, concentrating, drying and packaging. According to the yak, cow and ewe three-in-one composite infant formula milk powder, the yak milk, the cow milk and the ewe milk are added according to a reasonable ratio to be used as main ingredients, the purposes of achieving nutritional complementarity and mutually making up deficiencies are achieved, the nutrition ingredients tend to be more reasonable, and the growth and development needs of infants can be met to the greatest degree.