Different from chemical adsorption, physical adsorption depends on the interaction of Van der Waals force, but not chemical bond, between the adsorbent surface atomy and the adsorbate molecule. And the physical adsorbent in the adsorption refrigeration system always works in the vacuum environment where is much clean. Therefore, it is generally believed that only completely reversible physical change occurs in both adsorption process and desorption process, and there is no adsorption deterioration of physical adsorbent as similar as that of chemical adsorbent [89]. Actually, there is no clear boundary between physical adsorption and chemical adsorption. Both chemical change and physical change exists in the adsorption and desorption process of chemical adsorbent and physical adsorbent [90]. And such chemical change in adsorbent might not be completely reversible. The slight irreversible chemical changes are cumulated to result in the changes of the surface characteristics and the structure of the physical adsorbent so that the adsorption capacity of the adsorbent decreases with the time and the cycle times, so-called adsorption deterioration. In the following discussions, silica gel–water system is taken for an example to analyze the adsorption deterioration in physical adsorption refrigeration.