A series of polyaluminum silicate chlorides (PASC), which have different OH_/Al and Al/Si molar ratios, has been repared by a copolymerization technique and a compositetechnique, after which the coagulation efficiency and the residual aluminum content of PASC for water treatment were compared with polyaluminum chloride (PAC) by jar test. The experimental results show that PASC has better coagulation efficiency and lower residual aluminum content than PAC, and the PASC prepared by the copolymerization technique gives a better coagulating effect than that prepared by the composite technique. In addition, the OH_/Al and Al/Si molar ratios have some effect on the coagulation effect and residual aluminum content of PASC in treated water. With increasing OH_/Al molar ratio and decreasing Al/Si molar ratio, the residual turbidity and residual aluminum content in treated water diminishes. The pH of the water sample also affects the residual aluminum content of the water and there is a lower residua aluminum content in the neutral pH range.