Abstract: Kaolin is a low-cost and abundant resource in nature. Its product, superfine kaolin, was used as additive to prepare CaO-kaolin complex sulfur fixing reagent. The sulfur fixing efficiency of CaO-kaolin is studied by thermogravimetric technique. The results are compared to that of CaO. The conversion of CaO in CaO-kaolin is improved much more than that of pure CaO by 26% when reacting at 100 9 ℃. The grain model of reaction kinetics is used to describe the sulfur fixing process of CaO-kaolin. Because of increasing synchronously, the kinetic data of activation energy Ea and the gene k0 can't reflect the activity of sulfur fixing reaction. Reaction velocity k, diffusion coefficient DS of CaO and CaO-kaolin at different temperatures show that CaO-kaolin has better reaction performance because kaolin greatly improves the diffusion coefficient DS.