The invention discloses a slope, pit bottom and foundation bottom seepage preventing method based on a tailings composite anti-seepage material. The used tailings composite anti-seepage material comprises, by mass percentage, 3.3-4.8% of stabilizer, 3.3-4.8% of wetting agent, 10.0-15.2% of sodium silicate, 10.0-15.2% of cement and 60.0-73.0% of tailings slurry, wherein the stabilizer is the mixture of calcium chloride and sodium borate tetrahydrate, The method includes: preparing and mixing the anti-seepage material, processing a to-be-sprayed face, conveying the mixed anti-seepage material, spraying the mixed anti-seepage material, and inspecting spraying quality. The method has the advantages that an anti-seepage material layer finally formed by the method is extremely low in permeability, the permeability of the anti-seepage material layer is only 1 / 1000 of that of high-quality clay, the permeability coefficient k of the anti-seepage material layer can reach 1*10<-9>, and the anti-seepage material layer is good in acid resistance and base resistance, high in stability, high in concretion strength and resistant to erosion.