This invention relates to a preparation of crystal whisker of calcium sulfate, particularly relating a preparation that produces fibriform mon-crystal of half water or dried gypsum, its concrete steps as following: (1) Adopt hydrothermal synthesis etc technology to compose target agent of crystallizing; (2) Firstly calcium oxide that is technica grade is pretreated, added into reaction vessel to digest at 40-60DEG C, calcarea galacta is obtained; (3) The calcarea galacta that is obtained raises temperature to 40-110DEG C in reaction vessel, add equimolar solution of sulphuric acid, mix 30-60min,add targeting agent of crystallizing in reaction process. Make it react sufficiently, obtain products of required crystal whisker of calcium sulfate by filtering, cleaning, surface treatment and drying. Characteristic of this invention is: add targeting agent of crystallizing that is self produced, control different reactive temperature, obtain crystal whisker of calcium sulfate with different dolicho- diameter ratio, dolicho- diameter of this product is uniform, dolicho- diameter ratio is large, purity of raw material has no strict requirement.