Improved technology for decomposing gypsum outside a kiln for preparing sulfuric acid and cement clinker features that typsum may be decomposed cyclically in fluidized bed type reactor in decomposing furnace. Invented equipment is composed of cyclone preheating system and main body of decomposing furnace consisting of jmain reactor, deflected conical type cyclone separator and solid classifier. The time when gypsum powder stays in main reactor is 20-60 seconds and decomposed solid quantity returned to main reactor from solid classifier is about 70-90%.