The invention discloses alum-free potato nutritional vermicelli and a preparation method thereof. The preparation method comprises the following steps: compounding and mixing potato starch and a defined amount of cassava modified starch according to a formula, pasting and pulping the compounded starch together with vegetable powder and other auxiliary materials as required, vacuumizing, forming and steaming, cooling, freezing, vertically slitting, drying, transversely slitting and packaging to obtain the alum-free potato nutritional vermicelli. The alum-free potato nutritional vermicelli comprises the following components in parts by weight: 70-95 parts of potato starch, 30-5 parts of cassava modified starch, 2-8 parts of vegetable powder, 0.01-0.05 part of compound salt and a proper amount of water. Due to the addition of the cassava modified starch, the alum-free potato nutritional vermicelli is high in toughness, high in boiling resistance, delicious in taste and free from alum; the vegetable powder comprises spinach powder, celery powder, tomato powder, pumpkin powder, beet powder, carrot powder, cucumber powder, barley grass powder and the like, and the vegetables contain different nutritional ingredients, so that the nutritive value of the vermicelli can be improved, the problems that existing vermicelli is single in variety, ingredient and trophic structure are also solved, and good economic benefits and social benefits are obtained.