The invention provides a method for preparing a geopolymer gel material and geopolymer mortar. The method comprises the following steps: carrying out drying, and fine grinding pre-treatment on fly ash; taking the pre-treated fly ash, mineral slag powder and a compound exciting agent according to the Si/Al mol ratio of 2.40 to 3.35, the Na/Si mol ratio of 0.30 to 0.50 and the Ca/Si mol ratio whichis less than or equal to 0.95, and uniformly mixing; adding blending water according to the mass ratio of the blending water to the sum of the fly ash and the mineral slag powder of 0.20 to 0.40, so as to obtain a neat paste mixture; filling the neat paste mixture into a mold; after curing the mold for 12 hours to 72 hours under the conditions that the temperature is 20 DEG C to 80 DEG C and the relative humidity is 50 percent to 95 percent, de-molding; after curing a de-molded test piece, obtaining the geopolymer gel material. According to the method provided by the invention, the combustionfly ash of domestic garbage and the mineral slag powder are used as gel components to produce and prepare the novel geopolymer gel material, and treatment and resource utilization of the fly ash are realized.