The pretreated desulfurization gypsum was used as raw material, the sulfuric acid was used to adjust the pH value of the reaction solution, and the desulfurization gypsum whiskers were prepared by hydrothermal method to realize green production. Through the recycling of filtrate with or without reagent compensation, the effect of cycle number of filtrate on the quality of whiskers, pH value of solution and concentration of Na+ was studied. The results show that, with the increase of cycle number of filtrate, the pH value of filtrate gradually increases, but the concentration of Na+ decreases and its loss is from 27.3% to 34.6% in the condition of no reagent compensation. When H2SO4 and NaCl are used to compensate the reaction solution, the effect of cycle number of filtrate on the concentration of Ca2+ is slight before and after reaction. However, the cycle number of filtrate has an obviously effect on the crystal morphology, aspect ratio and quality of whiskers. When the cycle number of filtrate is less than 5, the quality of prepared whiskers is relatively good.