Calcium sulfate whiskers were prepared by hydrothermal synthesis method with desulfurized gypsum as raw material. The effects of acidification pretreatment, slurry concentration and reaction temperature on the preparation of calcium sulfate whiskers were studied by X-ray diffractometer, scanning electron microscope, energy spectrometer, thermal gravimetric analyzer and other test methods. The experimental results show that the acidification pretreatment effectively removes CaCO3 impurities in raw materials. As the slurry concentration and reaction temperature increase, the aspect ratio of whisker increases first and then decreases. When the slurry concentration is 3%(mass fraction), the pH value is 6.5, the reaction temperature is 120 ℃ and the reaction time is 2 h, calcium sulfate whiskers achieve the best average length of 161.2 μm, and the best average aspect ratio of 46.06.