Abstract: Hydrofluorosilicic acid,by-product of phosphate fertilizer production and low cost kaolin ware applied to substitute aluminum hydroxide,and relatively deficient fluorite resource to produce aluminum fluoride.Experiments showed the optimum leaching process conditions:Al<SUB>2</SUB>O<SUB>3</SUB> of kaolin was 26%~30% （mass fraction）,H<SUB>2</SUB>SiF<SUB>6 </SUB>of hydrofluorosilicic acid was 21%~28%,leaching temperature was 80~100 ℃,leaching time was 10 min and pH of reaction terminal was at 1~4.Aluminum fluoride with 20%~25% of the generated product should be added at the first crystallization as seed crystal.Meanwhile,to reduce iron content of finished product after crystallization,sodium thiosulfate was added into the solution before crystallization to eliminate Fe<SUP>3+</SUP>.Crystallization temperature and crystallization time controlled at about 90 ℃ and 5 h respectively,were the best reaction conditions.This method not only reduces the cost of production but also releases the environmental pressure of phosphate fertilizer plant. Therefore,it has a certain social and economic-benefits.