Provided is a method for preparing manganese sulfate monohydrate by desulfurizing fume with middle-low grade manganese dioxide ore, which comprises: preparing a slurry by using middle-low grade manganese dioxide ore powder, first putting sulfur-containing fume in an absorbing device and controlling gas velocity and gas-liquid ratio, and then adding manganese dioxide slurry and controlling the slurry to backwards flow relative to the sulfur-containing fume, discharging the desulfurized fume from the absorbing device, pressure-filtering and separating the slurry discharged from the absorbing device, recycling the mother liquor to the absorbing device, and continuing the recycling operation until the manganese sulfate in the mother liquor is >=200g/l, agitating and washing the obtained filter cake at 60-70°C, adjusting pH value of the clear solution obtained by pressure-filtering and separating to 2-4, adding manganese sulfide under agitation at 25-95 °C, and filtering and removing impurities, continuing agitating, pressure-filtering and separating, vaporizing the obtained clear filtrate, and obtaining manganese sulfate monohydrate after drying in the air stream. Desulfurizing efficiency is improved, the production cost of manganese sulfate is reduced, the recycling rate of total manganese is improved, and the valuable metals are recycled in high efficiency.