Calcium sulfate dehydrate is also known as "natural anhydrite". Chemical formula is CaSO4. The molecular weight is 136.14. It is rhombic system crystal. The relative density is 2.960, refractive index is 1.569,1.575,1.613. Another is soluble anhydrite: melting point is 1450oC, the relative density is 2.89, refractive index is 1.505,1.548, When be incandescent, it can decompose. Its hemihydrate is commonly known as "plaster of Paris", "plaster", it is white amorphous powder, relative density is 2.75. Its dehydrate is commonly known as "gypsum", as a white crystal or powder, relative density is 2.32, refractive index is 1.521,1.523,1.530, when be heated to 163oC, it can lose all crystal water. It is slightly soluble in water, hydrochloric acid, nitric acid, it is soluble in hot sulfuric acid, it is insoluble in alcohol. Natural product is soluble in alkaline sulphates, sodium thiosulfate, aqueous solution of ammonium salt. Method: natural anhydrite is derived by the reaction of CaO with SO3 under red-hot. Soluble anhydrous gypsum is derived by CaSO4·2H2O which heated at 200oC to constant. Hemihydrate gypsum is derived by the calcination dehydration. Dihydrate is reacted by calcium chloride and ammonium sulfate. The main purpose of calcium sulphate: natural anhydrite is used for medicine; soluble anhydrite can be used for interior decoration, it can also be used to prepare chemicals, beverages, etc; hemihydrate is used for construction materials, but also can be used in plaster statues, ceramics material; its dihydrate is used to product hemihydrate, fillers, etc. (1) Calcium sulfate dihydrate can be used as raw material of building materials and cement, it can also be widely used in rubber, plastics, fertilizers, pesticides, paints, textiles, food, pharmaceutical, paper, household chemicals, arts and crafts, culture and education sectors. In the areas of absence of sulfur resource Calcium sulfate dihydrate can be used to manufacture sulfuric acid and ammonium sulfate. Colorless and transparent gypsum can be used for optical materials. (2) Calcium sulfate dihydrate can be used as raw material of manufacturing cement, calcium sulfate hemihydrate and sulfuric acid. Paint and paper industry can be used as fillers. It can be used as fertilizer in agriculture which can reduce the alkalinity of the soil, improve soil properties. Food grade can be used as nutritional supplements (calcium to strengthen), coagulants, yeast food, the dough adjusting agents, chelating agents, it can also be used as enhancer of tomatoes, potatoes, canned organizations, hardener of brewing water, flavor-enhancer of wine, etc. (3) Calcium sulfate dihydrate can be used as hygroscopic agent of analysis of trace nitrogen fertilizer production of carbon dioxide and carbon monoxide and carbon dioxide. It can be used in paint, artificial ivory, paint, paper, dyes, printing, metallurgy, water treatment.