The invention relates to a yeast protein and a preparation method thereof, a food prepared from the protein as a raw material and a preparation method thereof. The yeast protein comprises by weight, 50-80% of a protein, carbohydrate, fat, 0.1-1.5% of nucleic acid, moisture and ash. The preparation method of the yeast protein is as below: low nucleic acid yeast is used as a raw material, and subjected to processes comprising superfine grinding treatment, enzymatic hydrolysis, alkali treatment, acid precipitation, centrifugation, washing and spray drying. The food containing the yeast protein comprises the following raw materials by weight: 20-80% of a soybean protein, 1-40% of the yeast protein, and 1-40% of a whey protein. The food is prepared by steps of component mixing, granulation, drying, sieving and packaging. The food is an excellent protein nutrition, and has high protein biological utilization rate; and the protein has acid amino composition ratio quite similar to that of human body, and is a high-quality protein and suitable for body absorption.