The invention belongs to the field of food processing technology, and particularly relates to a vegetarian nutritional powder and a preparation method thereof. The vegetarian nutritional powder comprises cooked cereal powder, a nutrition regulating agent, and a flavor regulating agent, wherein the granularity of 80% of nutritional powder is smaller than 120 meshes, and the granularity of 100% of nutritional powder is smaller than 100 meshes; the content of protein is greater than 20%, the content of GABA (gamma-aminobutyric acid) is greater than 500mg/100g, and the content of VB (vitamin B) isgreater than 2mg/100g; the cereals comprise grains and potatoes, the grains comprise brown rice, corn, millet, coix seeds, oats, barley, green beans, red beans, black beans and polished rice, and thepotatoes comprise yam, lotus root, and kudzu root. The preparation process comprises the following steps of (1) cleaning of the raw materials; (2) nutrition conditioning; (3) drying; (4) crushing; (5) nutrition and flavor compounding; (6) bacteria reduction; (7) packaging. The vegetarian nutritional powder has the characteristics that the target nutrients are enriched through nutrition conditioning, so that the target nutrients can fully meet the requirements; the vegetarian nutritional powder is uniform and fine, the solubility is good, the absorption effect is good, the mouth feel is good,and the like; any artificial synthesis matter is not manually added in the processing process, and the healthier effect is realized.