This invention is a preparation method of calcium sulfate crystal whisker. The material is plaster stone (CaSO4.2H2O) and water in the entire production. After raw material preparation, building up reactions, dehydrate, refine and edulcoration. Its characteristic is that the active content of plaster stone up to above 95%, the whiteness is above 90%. Mixed with water and turn into plaster stone slime, then put them into reactor to make them have chemical reaction, then on the other procedures. The calcium sulfate crystal whisker made by this method has good performance, low cost, and can be used in all kinds of industries.