Abstract: In view of the technical problems of large energy consumption and high cost in the operation of the wet desulfurization system ina 1 000 MW ultra-supercritical boiler,the SO_2 and O_2 concentration on the inlet and outlet of the flue gas desulfurization system was meas-ured timely by using a NGA2000-MLT3 type flue gas analyzer,the desulfurization efficiency of the system was obtained,and the operation-costs including limestone,SO_2 discharge fee and the main equipment power consumption of desulfurization system during the test were cal-culated or tested. According to the test results,the effect of the slurry circulating pump combination mode,pH value of the slurry liquid and the liquid level of absorber on the desulfurization efficiency were studied respectively. The desulfurization cost was calculated according tothe operation condition of the unit during the test period,and the optimum operation mode of the desulfurization system was obtained. Theresults indicate that during the operation process,when slurry circulating pump combination of BD is used,the SO_2 concentration at outletof the chimney is low,but the power consumption of slurry circulating pump is high under 1 000 MW load. When choosing the slurry circu-lating pump combination of BC,the costs are moderate,the desulfurization efficiency of absorption tower can reach 97.06%,and there is a margin of SO_2 concentration at outlet of the chimney at the same time,therefore the optimal choice of slurry circulating pump combinationunder 1 000 MW is BC. A high pH value of slurry in the absorption tower is not conducive to the dissolution of limestone,while when thepH value is too low,the SO_2 absorption rate decreases. The test results show that the best pH value of slurry is in the range of 5.50-5.60 under 1 000 MW and the slurry circulating pump combination of BC. As the pH value is further reduced,SO_2 emissions will exceed thelimit of power plant emissions. The level of the absorption tower has an important influence on the costs of desulfurization system. The riseof the absorption tower level can improve the desulfurization efficiency of the system,but the power consumption of the oxidation fan will beincreased. The effect of absorption tower level on the total operation cost of the desulphurization system was experimentally studied by con-tinuously adjusting the absorption tower level. The results show that the best liquid level of absorber is from 8.00 m to 9.00 m with the bestslurry circulating pump combinations and the pH value. The total cost of the desulfurization system decreases from 2 010.45 yuan/h to1 916.65 yuan/h,which is 9.64% reduction,as the absorption tower level is reduced from 9.53 m to 9.01 m.