The invention discloses a glycosylated yak casein and a preparation method thereof. After the yak casein is modified by glycosylation, the solubility and the processibility of the yak casein can be improved. The product produced from the glycosylated yak casein by use of the method is better digested and absorbed by a human body, so that the human body can absorb the nutritional ingredients of the yak casein more efficiently. The glycosylated yak casein is spray-dried so as to be preserved and transported more favorably, and can be better applied to industrial production. The preparation method is simple and feasible, and advantageous for controlling the product quality in the practical production and processing, and has an important popularization and application value.