The invention relates to the deep processing field of soy bean protein. Specifically, the present invention relates to an acid soluble soy protein preparation method which includes the following steps: alkali dissolving, acid precipitating and centrifugating a defatted soy bean residue to obtain soybean protein isolate precipitation which is dissolved in water to form a slurry, adjusting the pH of the slurry to 1.0 to 4.0 using an acidity regulator, stirring and completely dissolving the soybean protein isolate precipitation to obtain a protein liquid a; microwave digesting the protein liquid a and separating the protein liquid a through centrifugation; treating supernatants obtained by centrifugation at a temperature of 100-180 DEG C and subsequently cooling the treated supernatants; and at last, obtaining the acid soluble soy protein through spray drying. The acid soluble soy protein preparation method has the following advantages of high production efficiency, simple process, low production cost, and high product safety; and produced acid soluble soy protein has a relatively high solubility in the acidic region, and thus acidic beverage containing the acid soluble soy protein has less precipitation, a good taste and a high nutritional value.