The invention discloses a method for producing a calcium sulfate whisker by pretreating desulphurization gypsum through ionic liquid. The method comprises the steps of mixing a desulphurization gypsum raw material and a [Bmin][PF6] ionic liquid at room temperature and extracting heavy metals; separating, carrying out burning and grinding, carrying out hydrothermal reaction and controlling the pH value of a system, filtering while the solution is hot to obtain a calcium sulfate whisker precursor of which the length-diameter ratio is (100-200):1; obtaining a high-quality calcium sulfate whisker through a recrystallization mode. The method has the advantages that heavy metals such as Ni, Cu and Pb in the desulphurization gypsum are effectively removed through pretreatment of the ionic liquid; the introduced pH modifier is capable of promoting the growth of the whisker under the condition of ensuring the purity of the system; and the ionic liquid can be reused after vacuum concentration. In addition, the required equipment is simple, the process is simple and convenient, the additional environmental hazard is not caused, the resource utilization of desulphurization gypsum wastes is achieved, and the method has extremely profound social meaning and economic value.