4A molecular sieve, is an alkali metal silicaluminate, pore size 4A, is A type A crystal structure of sodium type. Adsorption of water, methanol, ethanol, ethylene, propylene, hydrogen sulfide, sulfur dioxide, carbon dioxide, ammonia and other critical diameter is not greater than 4A of any molecule. Its selective adsorption of water is higher than other molecules. 4A molecular sieve, pore size distribution is very uniform, has very good adsorption performance and good oil adhesion, safe and reliable for human body, no adverse impact on the ecology. In a high temperature or very low humidity environment, it can ensure that the adsorption capacity of water exceeds that of other desiccant.