Activated alumina is a porous, highly dispersed solid material with high specific surface area. Its microporous structure has the characteristics required by catalysis, such as adsorption, surface acidity and thermal stability. Activated alumina is widely used in industry, mainly as desiccant, adsorbent, catalyst and catalyst carrier. Alumina catalysts are mainly used for olefin isomerization and hydrogen and heavy hydrogen exchange (i.e. hydrogenation and dehydrogenation), and can also be used as new catalysts for sulfur recovery from acid gas in refineries. In addition, the composite catalysts consisting of alumina, various metals and metal oxides are widely used. The production and modification of activated alumina are analyzed in this paper. Activated alumina is an excellent desiccant. Alumina used as desiccant has large specific surface area. It is widely used for spherical particles with diameter of 3-5 mm and 6-8 mm. Activated alumina can absorb a large amount of water vapor, and water-saturated alumina can be easily reused by drying the physical adsorbed water. In addition to dry air, activated alumina is also used to remove moisture from various gases and organic liquids, such as alcohol dehydration. Activated alumina is also a good adsorbent for oxides of ammonia, hydrogen fluoride and arsenic. It has been widely used as a high-quality fluoride removal agent for drinking water with high fluoride content and as an arsenic removal agent for acid making industry.