Vacuum freeze-drying technology is also known as sublimation drying. The principle is to freeze a sample containing water in advance, and then sublimate its moisture under vacuum. The original biological, chemical and physical properties of the freeze-dried samples remain basically the same, and they are easy to be stored for a long time. After adding water, the samples can be restored to the state before freeze-drying, and their original biochemical characteristics can be maintained. Therefore, freeze-drying technology is widely used in medicine, food, chemical, biological products and other fields.