Abstract: A series of polyaluminum silicate sulfate (PASiS) with different basicities, Al/Si molar ratios and silicic acid polymerization degrees was prepared by the copolymerization (COPOLY) and composite polymerization (COMPOLY) techniques. The distribution of aluminum species in PASiS, the charged characteristic of its hydrolysis products and their affecting factors were investigated by the Al-Ferron timed complex colorimetric method and the micro-electrophoresis method. In addition, the interaction between polysilicic acid and hydrolysis aluminum species in PASiS was discussed. The experimental results of water treatment show that the flocculation effect of PASiS is better than polyaluminum chloride, polyaluminum sulfate, polyaluminum sulfate- chloride and polyacrylamide, and PASiS (COPOLY) is better than PASiS (COMPOLY). The flocculation properties of PASiS are related to the basicity, Al/Si molar ratio and polymerization degree. The adsorbing-bridging and entrapping-settling are the principal mechanisms of PASiS functioning.