The invention discloses an 
alum-free pure sweet 
potato starch vermicelli and a preparation method thereof. Sweet potato native 
starch in product formula is subjected to denaturating treatment to obtain sweet potato denaturated 
starch, starchy sauce preparing, kneading dough, pasting, maturing, strip 
cutting and 
drying are performed by denaturated sweet 
potato starch and other auxiliary materials according to the preparation method of the vermicelli to obtain the 
alum-free pure sweet 
potato starch vermicelli product, and the 
alum-free pure sweet potato 
starch vermicelli product comprises, by weight, 100 parts of sweet potato native starch, 0.08 to 0.3 part of 
sodium trimetaphosphate, 0.1 to 0.5 part of 
sodium hexametaphosphate, 0.1 to 1 part of 
sodium carbonate, 0.2 to 0.8 part of 
sucrose fatty acid ester and an appropriate amount of water. According to the alum-free pure sweet potato starch vermicelli and the preparation method thereof, the sweet potato native starch is subjected to denaturating treatment, so that insoluble 
amylase of the sweet potato starch is added, the vermicelli is toughened, boil-resistant, nutritious and free of alum and tastes good, the quality guarantee period of the product is long, requirements of users for healthy and safe foods can be met, the vermicelli is suitable for people of all ages and both sexes, and good economic and 
social benefits are achieved.