Calcium sulfate whisker(CSW) was prepared from phosphogypsum. Crystallization behavior of CSW was studied in four aspects of solid-liquid ratio, concentration of solvent, temperature and cooling rate. Phosphogypsum and CSW were tested, and the effects of experimental conditions on length, length-diameter ratio and morphology of CSW were determined by microscopic observation and image analysis. Crystallization behavior was analyzed based on crystallography. Some conclusions have been reached:With the increase of solid-liquid ratio, the length and length-diameter ratio decreased first and then increased; with the increase of the concentration of solvent, the length-diameter ratio increased; with the increase of temperature and cooling rate, the length-diameter decreased. The average length of whisker is between 200μm and 400μm, and the average length-diameter ratio is between 25 and 30. The change of length and length-diameter ratio can reflect the change of the morphology of the whiskers. Crystallization behavior of the whiskers is divided into two stages:the formation of crystal nucleus and the growth of the whisker. The experimental conditions affect the crystallization by influencing the nucleation rate, degree of supersaturation and the solution of phosphogypsum.