Abstract: The present invention discloses a method for adsorption and immobilization of a heavy metal ion in water and a method for preparing a geopolymer cementitious material, and belongs to the fields of environmental protection engineering and materials engineering. The method for adsorption and immobilization of a heavy metal ion in water includes the following steps: adsorbing a heavy metal ion in water using carbonized micropowder; mixing the carbonized micropowder after adsorbing the heavy metal ion with one or more of granulated blast furnace slag, gypsum, and steel slag to obtain a solid material; and mixing the solid material with an alkaline activator, followed by curing and molding. According to the present invention, a solidification amount of heavy metals can be significantly increased. Meanwhile, a prepared geopolymer has excellent mechanical performance, can be used as a low-cost green building material or for fields such as solid waste landfill.