The calcium sulfate dihydrate whiskers (CSW) were prepared using rare earth gypsum as raw material, and the effects of preparation methods on the morphology and structure of CSW were studied. The effect of rare earth cerium on the structure and morphology of CSW was investigated using pure calcium sulfate dihydrate as raw material and CeCl3·7H2O as cerium source. The structure, morphology, composition, and fluorescence properties of CSW were characterized and analyzed by SEM, XRD, XPS and FL. The results show that calcium sulfate dihydrate whiskers with high aspect ratio can be prepared by microwave method, with average length of 263 μm and average aspect ratio of 39.50. Ce3+ enters CSW in the form of atomic substitution during the formation of CSW, which does not affect the crystal structure of CSW, but improves the morphology of CSW. When 2% (mass fraction) Ce3+ is added, one-dimensional growth of CSW is promoted to make the aspect ratio of CSW increase significantly, while excessive Ce3+ leads to the growth of whiskers in the transverse direction. This study proves that rare earth gypsum contains trace amounts of rare earth element Ce. At the same time, it is found that CSW prepared from rare earth gypsum presents the characteristics of emitting blue light, which provides theoretical guidance for the development and utilization of rare earth gypsum.