The invention provides a preparation method of a dried onion which comprises the following steps: a. removing a peel of fresh onion, washing and shredding into 2-4cm, dehydrating to 40-55%; b, weighing raw materials according to weight ratio; c. stirring uniformly the raw materials weighed in the step b, sealing for 8-12 months, controlling the temperature between 5-25 DEG C, and vacuum packaging. The dried onion prepared through natural fermentation and by using the preparation method of the invention not only keeps various nutrition ingredient of the onion, has special, faint scent and crisp and sweet taste, can be edible for a long time, but also has health care effect and provides a new choice for consumers.