When heating and calcining the dihydrate gypsum, the dihydrate gypsum will be decomposed, we can produce the semi-hydrated gypsum (CaSO4?/2H2O) , that is building gypsum, also called plaster of paris. Because of the different temperature and pressure when decompose the gypsum, we can get different product, a-type gypsum and b-type gypsum. a-type gypsum is high-strength gypsum,b-type gypsum is building gypsum. They are the same technology using mechanisation producing building gypsum. The process can be divided into three system, crashing system, calcining system and milling system.