In order to solve the sliding failure problem caused by the wet expansion and dry shrinkage of expansive soil in the North Xinjiang water supply project, lime, cement and sand and gravel were used as the main curing materials. Through unconfined compressive strength test, direct shear test, compression test and SEM test, the influence of test dosage on the mechanical properties of improved expansive soil and the formation mechanism of microstructure strength under different improvement methods were studied by combining macro and micro. The test results show that with the continuous increase of the amount of lime and sand gravel, the soil strength increases steadily, while the peak value of cement improved soil appears when the amount of lime and sand gravel is about 7%. For lime and sand gravel, when the amount of lime and sand gravel is about 6% and 30% respectively, the overall compressibility of the improved soil is low, the cohesion is large, and the shear and compressive strength is high, which can meet the requirements of engineering application. The SEM analysis of lime and cement stabilized soil with the best mix ratio shows that a large number of curly flake hydrated gel materials are generated, which significantly reduces the pores compared with the original expansive soil, and the aggregates are closely cemented. From the macro mechanical properties, the mechanical properties and stability of the solidified soil are greatly improved.