The wet-based desulfurization gypsum is sent to the φ3×25m high-efficiency rotary dryer by the double screw feeder and tape conveyor for drying and removing the physical water. The dryer adopts high-temperature flue gas to provide a heat source, and the exhaust gas of the dryer is discharged after being collected by the high-temperature gas box pulse bag dust collector. Out of the dryer dry desulfurization gypsum (CaSO4·2H2O) sent to the Fahrenheit mill for grinding, out of the mill after screening, sent to the boiling calcination, desulfurization gypsum after boiling calcination by two crystal water degenerated into half of the crystal water, to make mature gypsum powder (CaSO4·1/2H2O), that is, desulfurization gypsum powder, usually white, colorless, colorless transparent crystals called hydrated gypsum, sometimes due to impurities into gray, light yellow, light brown and other colors. The streaks are white. Transparent. Vitreous luster, cleavage surface pearl luster, fibrous aggregate silk luster, relative density 2.3.