Geopolymer has the advantages of fast hardening, early strength, and good durability, and it is an ideal agent for soil improvement. However, their reasonable material ratio design significantly controls the expected engineering performance of geopolymer improved soil. Taking metakaolin as the precursor for preparing geopolymer materials, in which the quicklime and sodium silicate was selected as the alkali excitation materials. A series of mechanical tests of geopolymer improved soils with different material ratios was carried out to investigate the ideal material ratio design of the geopolymer, analyze the optimal content of geopolymer for soil improvement, discuss the influence of basalt fiber content and length on the performance of geopolymer improved soil, and comprehensively evaluate the solidification effect of geopolymer and fiber on the soil. The results showed that the mechanical properties of geopolymer and fiber stabilized soils were improved first and then weakened with the increase of geopolymer content, fiber content, and fiber length. When the mixing ratio of metakaolin and alkali activator was 2:1, the mixing ratio of sodium silicate and quicklime in alkali activator was 1:0.8, the total mixing ratio of geopolymer in soil was 15%, and the mixing amount and length of basalt fiber were 0.4% and 12 mm, the mechanical improvement of geopolymer and fiber improved soil was the best. The solidification comparison test shows that the geopolymer and fiber improved soil was superior to ordinary cement soil, lime soil, and pure clay in compressive, tensile, and shear strength. The research results can provide a reference for soil improvement using geopolymer and fiber.