The invention relates to a cultivation method for purple sweet potatoes and a method for processing purple sweet potato powder and belongs to the technical fields of sweet potato cultivation and processing. A new cultivation method is obtained by changing the concentration of thiophanate methyl water solution for soaking seeds, sweet potato seedling planting time and density, fertilizer types and consumption, and types and concentration of inhibitors. According to the cultivation method, acre yield of fresh potatoes is more than 2,200kg, the large medium sized tuber rate is higher than 90.3 percent, anthocyanin content is more than 120mg/100g, and starch content is more than 31.1 percent; the yield for preparing the purple sweet potato powder from the purple sweet potatoes harvested by the cultivation method is higher than 41.6 percent. Methods of cooking, mashing, drying and pulverizing are adopted, sweet potatoes are sliced, and the sliced sweet potatoes are blanched, cooled, cooked, mashed, dried, pulverized and screened to form the purple sweet potato powder, the defect of poor cluster caused by improper color protection in the traditional process is overcome, and the processed product is bright in color, high in dispersibility and high in water absorption.