Abstract: This is a paper in the field of ceramics and composites. In order to understand the water content distribution characteristics of 4A molecular sieve in the process of water absorption and dehydration, the calculation methods of high temperature dehydration and low temperature water absorption were used to discuss the water content distribution of 4A molecular sieve under different desorption temperature and atmosphere. The results showed that when the desorption temperature was 200~230 ℃, the effective residual water was 4%~5%, the effective desorption water was 24%~25% and the water absorption was 83%~87% in the non vacuum air desorption under vacuum, the effective residual water was 1%~2%, the effective desorption water was 27%~28%, and the water absorption is 93%~97%. In order to make the effective residual water content less than 2%, the best desorption regeneration conditions are vacuum atmosphere and desorption temperature not less than 200 ℃.The effective dewater and residual water of molecular sieve in non vacuum atmosphere can be estimated by differential thermal analysis. The water absorption rate of the sample after vacuum desorption is higher than that of the sample without vacuum desorption.