Abstract: The preparation of poly-silicic ferric(PSF) coagulant was studied by level selection beforehand and mixing level and stepwise orthogonal design(LS-MLSO),in which different Si/Fe molar ratios of PSF were prepared by two different methods(method A and method B),respectively.The physicochemical characteristics,micro properties and coagulation efficiency of PSF prepared by method A were studied,in comparison with those of PSF prepared by method B.The results show that LS-MLSO is an efficient and reasonable method in the investigation of coagulant preparation.The physicochemical characteristics and micro properties of PSF prepared by method A was significantly different from those of PSF prepared by method B,in which various Si/Fe ratios of PSF prepared by method B have similar physicochemical characteristics and micro properties.PSF prepared by method A were characterized obviously by having higher coagulation behavior than PSF prepared by method A.