For example, tea moisture will affect the diffusion and transfer speed of substances and the interaction between substances, so water becomes a necessary condition for chemical reaction and Aspergillus reproduction, and water activity refers to free water. The higher the water activity, the lower the binding degree; The lower the water activity value, the higher the binding degree. The water content of tea has a great influence on the quality of tea. For example, when the water content of all kinds of crude tea is 6%~7%, green tea is 6.0-8.0%, and Tuocha is 9.5% [1], the quality is stable and its characteristics can be better exerted. When the water content exceeds 10%, mildew is easy to occur. When the water activity is lower than 0.6, most microorganisms cannot grow. Therefore, when the water content of tea leaves is controlled at 4%-6% during manufacturing and storage, its water activity is less than 0.6, which can effectively prevent microbial pollution of tea leaves.