First grind and second bake. The largest advantage of this technique, compared with that of “first bake and second grind”, is energy consumption reduction. Large plaster stone shall be ground into powders with diameter less than 0.2mm, which increases the specific surface when calcining, enlarges the contact area with heat medium, improves calcination heat exchange efficiency and lowers energy consumption greatly. This equipment has small bulk, large production capacity, and simple structure and is hard to destroy.