Abstract: Taking blast furnace slag as raw material and sodium hydroxide as solvent, aluminiferous hydrated sodium silicate was prepared via hyrothermal method. The effects of reaction temperature, sodium hydroxide concentration, reaction time and mass ratio of alkali to slag on the conversion rate of SiO₂ were researched. The results show that the optimum reaction conditions are as follows:the concentration of sodium hydroxide was 3.0 mol·L^-1, the alkali treatment temperature is 130℃, the mass ratio of sodium hydroxide to slag is 0.8, the reaction time is 4 h and the conversion rate of SiO₂ is 84.3%. Furthermore, taking the conversion rate of SiO₂ as index, the effects of reaction temperature, sodium hydroxide concentration, reaction time and mass ratio of alkali to slag on the conversion of SiO₂ were investigated via orthogonal experiment. The results show that the degree is in order of concentration of sodium hydroxide>alkali treatment temperature > ratio of alkali to slag > reaction time.