At present, zero discharge of high salinity desulphurization wastewater has become a bottleneck problem to be solved urgently in power plant, and flash-condensing-crystallization-curing of high salinity wastewater by using low temperature waste heat of unit is one of the key technologies to achieve zero discharge of desulphurization wastewater. In view of the problems caused by the unstable water quality condition, treatment capacity and heat source of desulphurization wastewater caused by variable load operation of the unit after the current grid-connected renewable energy such as wind and light, low efficiency of low-temperature residual heat flash concentration of desulphurization wastewater and easy scaling, etc., effects of low temperature negative pressure steam flow rate, wastewater treatment capacity, concentrated liquid ratio, wastewater recovery rate and other factors on the treatment of desulfurization wastewater by three-effect evaporator in the process of 60% to 100% variable load of the power plant was studied. According to the data analysis, the buffer tank should be set in front of the three-effect evaporation system to avoid system damage caused by excessive flow rate, and the wastewater recovery rate can reach 80%~90% when the system water intake is not more than 200 t/d. Low-temperature negative pressure steam flow fluctuates between 700 and 1 000 kg/h, so the flowmeter should be installed at the first condensate tank, and the low-temperature negative pressure steam production should be adjusted according to the water intake of the system, so as to avoid the waste of heat source caused by excessive low-temperature negative pressure steam production; in strict accordance with the density meter at the outlet of the three-effect evaporation system, the concentrated liquid is discharged immediately when the density reaches 1.35 g/mL. By the analysis of the condensate water generated during the stable operation of the three-effect evaporation system, the content of chloride ions reaches 1.56 mg/L, which can be used as the circulating supply water of the power plant. Besides, the daily power consumption of the system is 4 000 kWh. Without considering the personnel cost, depreciation cost, maintenance cost and other expenses, the cost of the three-effect evaporation system for treating 1 m3 of wastewater is 5-10 yuan.