The limestone desulfurization used is gypsum desulfurization, the limestone is made into lime powder by a sand washing machine, and then the water is pumped into the absorption tower to be fully contacted and mixed with the flue gas, and the calcium carbonate in the slurry and the lower part of the tower are blown into the slurry. The air is oxidized to form calcium sulfate, and after the calcium sulfate reaches a certain saturation, dihydrate gypsum is formed. The sand washing machine produced by integrates crushing, drying, grinding and grading and conveying. The system is simple and compact. The floor space is about 50% of the ball mill system, and it can be arranged in the open air, so it can greatly reduce the investment cost.