Abstract: Precipitated hydrated silica was prepared by secondary-neutralization method，and the influential factors of the product′s specific surface control were studied by single-factor experiments.Suitable factor combination was obtained：reaction temperature was 40 ℃，acid mass concentration was 70 g/L， alkali mass concentration was 110 g/L，acid adding ratio of the two stages（the proportion of the former acid dosage to the total acid dosage） was 70%，reaction time was at 60~120 min， and stirring rate was at 40~300 r/min.According to the production experiences，the law of the combinations of influential factors impacting the product′s specific surface was found，and the purpose of controlling the product′s quality through the accurate control of the specific surface of precipitated hydrated silica has been realized.

Key words: secondary-neutralization, precipitated hydrated silica, influential factors, specific surface control