A method for preparing manganese sulfate monohydrate by desulfurizing fume with middle-low grade manganese dioxide ore comprising the following steps: A. choosing manganese dioxide ore powder having a fineness between 80-100 mesh size obtained by treatment, preparing a slurry with an initial solid-liquid ratio of 10-30% in water or recycling mother liquor or liquid obtained from washing slag, so that MnO 2 content in the slurry is greater than or equal to 1.5% (percentage of weight); B. firstly putting sulfur-containing fume into an absorbing device based on controlling gas velocity between 0.5-4m/sec and gas-liquid ratio between 10-40 L/m 3, then adding the manganese dioxide slurry into the absorption device, controlling the slurry to backwards flow relative to the sulfur-containing fume, feeding the slurry into a separating procedure when manganese dioxide ore powder is reacted fully, and discharging the desulfurized fume from the absorbing device; C. pressure-filtering and separating the manganese dioxide slurry discharged in the step B, recycling the mother liquor obtained by pressure-filtering and separating to the absorbing device, evaporating and concentrating it in virtue of heat energy of the fume, and continuing the recycling operation until the concentration of manganese sulfate in the mother liquor becomes ≥200g/l; D. adjusting pH value of the clear solution obtained by pressure-filtering and separating in the step C to 2-4, controlling the temperature of the clear solution at 25 °C -95°C, adding manganese sulfide to react under agitation, filtering and removing impurities, continuously agitating for 1-1.5h and then pressure-filtering and separating, vaporizing the obtained clear filtrate, and drying obtained solid in the air stream to obtain manganese sulfate monohydrate product. A. choosing manganese dioxide ore powder having a fineness between 80-100 mesh size obtained by treatment, preparing a slurry with an initial solid-liquid ratio of 10-30% in water or recycling mother liquor or liquid obtained from washing slag, so that MnO 2 content in the slurry is greater than or equal to 1.5% (percentage of weight); B. firstly putting sulfur-containing fume into an absorbing device based on controlling gas velocity between 0.5-4m/sec and gas-liquid ratio between 10-40 L/m 3, then adding the manganese dioxide slurry into the absorption device, controlling the slurry to backwards flow relative to the sulfur-containing fume, feeding the slurry into a separating procedure when manganese dioxide ore powder is reacted fully, and discharging the desulfurized fume from the absorbing device; C. pressure-filtering and separating the manganese dioxide slurry discharged in the step B, recycling the mother liquor obtained by pressure-filtering and separating to the absorbing device, evaporating and concentrating it in virtue of heat energy of the fume, and continuing the recycling operation until the concentration of manganese sulfate in the mother liquor becomes ≥200g/l; D. adjusting pH value of the clear solution obtained by pressure-filtering and separating in the step C to 2-4, controlling the temperature of the clear solution at 25 °C -95°C, adding manganese sulfide to react under agitation, filtering and removing impurities, continuously agitating for 1-1.5h and then pressure-filtering and separating, vaporizing the obtained clear filtrate, and drying obtained solid in the air stream to obtain manganese sulfate monohydrate product.