In the limestone grinding classification operation of power plant, the ball mill and cyclone form a closed-circuit grinding classification system. The limestone ore is fed into the ball mill for grinding and discharging from the mill is pumped to the cyclone; the cyclone underflow returns to the ball mill to continue grinding, and the cyclone overflow enters into the next desulfurization operation as a qualified desulfurizer. Slurry concentration requirement on the cyclone overflow product is about 30% and the fineness is -325 mesh ≥ 90%.