Abstract: Pressure solution method and high temperature method are used to hydrothermal treatment desulfurization gypsum which is added crystal modifier preparing crystal α-hemihydrate decorative gypsum in the condition when the heating-up time is 90 min,and the autoclaved temperature is 130 ℃.The stereomicroscope and the WA-Y300 electronic hydraulic press are used to measure the morphology features and the compressive strength.The result demonstrates that when the heating-up time is too short or too long,it is not conducive to the improvement of strength.Only when saturation precipitated by α-hemihydrate decorative gypsum and growth rate reaches equilibrium,it is the best.When the autoclaves time is the best,the crystal transformation is most sufficient.And at this point the strength is the highest.Pouring time should be controlled in the time before α-hemihydrate decorative gypsum hydration,and the pouring temperature can be slightly lower than the autoclave temperature.The process of desulfurization gypsum preparing α-hemihydrate decorative gypsum by high temperature method is feasible.Heating-up time controlled within 90 min,6 h autoclaved compressive strength is up to 34.8 MPa.α-hemihydrate decorative gypsum paste pouring time should be about 2 minute and pouring temperature at 120 ℃ is the best.