The invention relates to a method for preparing acylated casein by taking yak milk casein as a raw material. The method comprises the following steps of: (1) preparing a casein solution, namely, dissolving the milk casein in deionized water, performing magnetic stirring till the complete dissolution of the casein, regulating pH value and stabilizing the pH value at 6.5-7.5 to obtain a casein solution; (2) acylating: regulating the pH value of the casein solution to 8.0-10.0, adding solid succinyl oxide in multiple times, performing constant-temperature magnetic stirring to perform succinylation, and continuously stirring for 30-50 min after the succinyl oxide is completely added so as to realize full reaction to obtain the casein solution after acylation; and (3) obtaining an acylated casein product: adjusting the pH value of the casein solution after acylation to an isoelectric point by adopting a hydrochloric acid solution to precipitate the casein, centrifuging to remove supernatant fluid to obtain a precipitate, and performing freeze-drying on the precipitate till constant weight to finally obtain the powdered white acylated casein product. The method disclosed by the invention is easy to control and good in modification effect.