Abstract: Fluosilicic acid as silica source and ammonium hydroxide as ammonia solution agent were used to synthesize high-quality nano-silicon dioxide and high content F- solution.The influence factor，such as the reaction temperature，feeding methods，aging time，and washing condition，on the preparation of silica dioxide was investigated.The optimum conditions for the synthesis of high-quality silicon dioxide were confirmed as follow：adding ammonia by 8 times to the product until the pH was at 8~9 at 40 ℃；the product was aged for 1 h，rinsed with a little alcohol after washed with water，and dried at 110 ℃ for  2 h after extraction, stewing, and volatilization.The nano-silicon dioxide with its mass fraction more than 93%，particle sizes of 89 nm and 322 nm，and the specific surface area is greater than 200 m2/g was obtained.The mass concentration of F- in solution was more than 90 g/L，and it′s benefit for comprehensive utilization.

Key words: fluosilicic acid, ammonium hydroxide, nano-silicon dioxide