Abstract: In response to the problem of poor effect of conventional single-method modification of expansive soil, this research team selected soil stabilizer and polypropylene fibers to improve the physical and mechanical properties of expansive soil and inhibit the expansion of internal fissures. The optimal dilution ratio of single-doped soil stabilizer and the optimal fiber dose of single-doped polypropylene fibers were obtained based on the free swelling rate, water stability test and unconfined compressive strength test. Meanwhile, the effect of soil stabilizer-polypropylene fibers composite improvement of expansive soil was analyzed under wet-dry cycling conditions based on macroscopic mechanical strength experiments and fine fracture and microscopic pore observation. From the experimental results, it can be obtained that the soil stabilizer can effectively reduce the free swelling rate of the expansive soil and enhance the water stability of the expansive soil, and the optimal dilution ratio (volume ratio) of the modified expansive soil is 1∶150. The reinforcing effect of polypropylene fibers can effectively improve the lateral limitless compressive strength of expanded soil, and the optimal fiber admixture is 0.20% (mass ratio). Polypropylene fibers and soil stabilizer can work together, and the unconfined compressive strength of the composite soil is effectively increased and the rate of strength decay is suppressed, and the expansion rate of fine and microscopic fractures of expanded soil is also effectively controlled. This study can provide reference for engineering application of soil stabilizer and polypropylene fiber composite to improve expansive soil.