Abstract: The species distribution and transformation characteristics ofpolysilicic acid in the presence of acetic acid were investigated by chemical Si-Mo assay analysis. The experimental results showed that in the acid condition the polymerization rate decreased in acetic acid media, and the contents of species Si_a and Si_b were increased. This further indicated that when the acetic acid compound existed it could slow the growth rate of the particles of polysilicic acid, but total species distribution and its transformation model ofpolysilicic acid did not change.