Abstract: There are two stages in the overall CaO Sulfation process: The initial stage of sulfation is chemical reaction control and its speed is faster. The second stage reaction proceeds under the product-layer-diffusion control regime after CaSO4 buildup. The later rate of sulfation is slower. It is very important how to improve the rate of the second stage of sulfation. The major process is that Ca2+ ions outward diffuse through the sulfate product layer to the surface of CaSO4 and react with O2－, O2 and SO2 other than they move inward to react with CaO covered by CaSO4, when the solid product layer CaSO4 of sulfation reaction is dense and not cracked. The CaSO4 covering and the pores in the CaO particles being plugged resist the further sulfation reaction. Hence, how to increase the rate of the further sulfation reaction is largely investigated. Several kinds of experiment technologies are performed to identify the mechanism of the Ca2+ diffusion. And a new mechanism greatly supports the result that the additives can obviously increase the overall conversion of CaO.