The invention discloses a method for synthesizing a high-efficiency environmental-protection filtering membrane. The method comprises the following steps: 1) mixing metakaolin and red mud according to the mass ratio of 0-2:8, adding phosphoric acid, wherein the mass ratio of phosphoric acid to red mud is 7-11:8 to obtain a geopolymer slurry; 2) mixing hydrogen peroxide (H2O2) and sodium dodecyl sulfate, adding water to prepare a foaming agent solution; 3) adding the foaming agent solution in the geopolymer slurry, stirring the materials to obtain the foamed geopolymer slurry, and performing post-treatment to obtain the product. According to the invention, an industrial alumina industry waste raw material red mud and metakaolin are taken as the main raw materials, the high-efficiency environmental-protection filtering membrane is synthesized by the simple synthetic method, the filtering membrane has the characteristics of effective adsorption of heavy metal ions, low cost, stable performance, and no secondary pollution; and the synthetic method can massively used for processing sewage and purifying rural drinking well water in chemical enterprises and sewage processing factories.