Water activity affects the shelf life, safety, texture, flavor, smell and stability of food. This measures the dryness enduring ability of the microorganisms in food samples. By measuring the water activity of food and selecting reasonable packing and storage methods, the use of preservatives can be reduced, and the shelf life of food, grains, fruits and vegetables can be judged. Widely useful in food, pharmaceutical, cosmetics, seed storage, tobacco industry, etc.