The main composition of gypsum is hydrate gypsum(CaSO₄.2H₂O). however, the gypsum powder used in practical production(such as the gypsum powder for gypsum board, for mould, for plastering)is to dry and dewater the dehydrate gypsum which of certain fineness, reduce the content of crystallization water in it, so the standard of crystallization of gypsum powder can qualify all kinds of gypsum powder, because it can change into plaster of pairs. Plaster of pairs can re-integrated with water when it is applied into production, and it can be processed into new type building materials with a high intensity, such as gypsum board, gypsum block, etc.

Existing gypsum powder drying technologies are frying boiler and rotary kiln plant. It means that put the gypsum powder into the frying boiler and coil pipe, and before the gypsum powder was put, the heat produced by the burning of the medium in kiln furnace was send into the frying boiler and rotary kiln plant by fan. In this way, the quality of gypsum powder is difficult to guarantee, because the content of crystallization water is uneven.