The invention discloses an 
improved method for preparing superfine high length-
diameter-ratio 
anhydrous calcium sulfate crystal whiskers by using a hydrothermal process and belongs to the technical field of preparation of 
inorganic chemical materials. The 
improved method for preparing the superfine high length-
diameter-ratio 
anhydrous calcium sulfate crystal whiskers by using the hydrothermal process takes 
calcium sulphate dihydrate as the 
raw material and comprises the following steps: firstly activating and 
roasting at the low temperature to prepare active calcium 
sulfate hemihydrates, subsequently 
doping, acidizing, hydrating and 
drying to prepare a quick-soluble calcium sulfate hemihydrates precursor with the structure defects; then adding the precursor into a saturated calcium sulphate liquid containing a 
chaotropic agent and a polar 
solvent, carrying out 
hydrothermal reaction at 100-200 DEG C for 2-20 minutes, cooling, filtering, washing and 
drying to prepare superfine high length-
diameter-ratio 
calcium sulfate hemihydrate crystal whiskers with diameter of 0.005-10 microns, length of 10-5000 microns, length-diameter-ratio of 100-10000, and main content of greater than 95%; then mixing the calcium sulfate hemihydrates crystal whiskers with a trace 
solvent, 
roasting at 600-800 DEG C for 1-6 hours, cooling, filtering, washing and 
drying to prepare the superfine high length-diameter-ratio 
anhydrous calcium sulfate crystal whiskers with appearance which is as same as that of the calcium sulfate hemihydrates crystal whiskers and main content of greater than 95wt%. The 
improved method for preparing the superfine high length-diameter-ratio 
anhydrous calcium sulfate crystal whiskers by using the hydrothermal process is rapid and simple in process and low in costs; and the prepared superfine high length-diameter-ratio 
anhydrous calcium sulfate crystal whiskers can be used as reinforcement materials.