Abstract: Hydrothermal synthesis was employed to prepare calcium sulfate whiskers (CSW) with desulphurized gypsum as raw material. The growth rules of CSW were investigated under different reaction conditions by virtue of chemical potential, electric conductivity, XRD and SEM. It was found that the aspect ratio of CSW tends to increase then decrease with increasing of the reaction temperature/time, solid-liquid ratio and initial pH value. The optimized process parameters as a result of the tests are the solid-liquid ratio is 1:10, initial pH value 5, raw material grain size 1.36μm and reaction temperature/time 140°C/120min, by which the aspect ratio of CSW may come up to 82.57.