The invention discloses a method for using flue gas desulfurization gypsum to prepare calcium sulfate whisker, comprising process steps of size mixing, high-temperature crystallization, drying and coating, etc. The method utilizes the flue gas desulfurization gypsum as the raw material, which has low production cost, short technological process and saves natural gypsum mine and effectively relieves the environmental pollution problem of the flue gas desulfurization gypsum. The product purity can be up to more than 98 percent, which can be used as filler with medium intensity or as friction material, building material or insulating material, and the like, instead of asbestos. The product can also partly replace organic macromolecular compounds such as glass fiber, resin, rubber and plastic, and the like, and has good describability.