Abstract: According to the characteristics of desulfurization wastewater in the coal-fired power plant, the desulfurization wastewater pretreatment method of the integrated softening and clarifying-ultrafiltration is proposed in this paper. The pilot project testing is completed in a coal-fired power plant in Shandong province. The study includes the removal efficiency of integrated softening and clarifying on Ca²⁺, Mg²⁺ and the turbidity, the operating pressure of the ultrafiltration system, the flow and turbidity of the product water, and the chemical cost of the pretreatment process. The results show that the content of Ca²⁺ decreases from 400~660 mg/L to 25 mg/L and the content of Mg²⁺ decreases from 5 310~15 689 mg/L to 10 mg/L after the treatment of desulphurization wastewater by integrated softening and clarifying-ultrafiltration, respectively, with the turbidity being no more than 2.0 NTU. The ultrafiltration system operates stably and the turbidity of product water is no more than 0.1 NTU, SDI value is less than 3.0, which can meet the required water quality conditions of the reverse osmosis system. The study results of the integrated softening and clarifying-ultrafiltration can provided important data for the research on the zero wastewater discharge technology in the power plant.