To investigate the mechanical properties of cement improved expansive soil under the action of different dry and wet cycles, direct shear and scanning electron microscopy tests of cement improved expansive soil under the action of different dosing, number of dry and wet cycles and amplitude of dry and wet cycles were conducted. The variation patterns of the number of wet and dry cycles, cement dosing, and the amplitude of wet and dry cycles on the shear strength, cohesion, and internal friction angle of the modified expansive soil were analyzed, and the mechanism of strength deterioration of modified expansive soils by the action of dry and wet cycles was also explored. The research results indicate that,the shear strength decay rate of the modified expansive soil tends to increase sharply in the early stage and slow down in the later stage with the increase of the number of wet and dry cycles. The shear strength of the modified expansive soil is positively correlated with the cement content compared to the unmodified expansive soil expansive soil, and the shear strength of the modified expansive soil with 8% cement admixture at 100 kPa for 0 wet and dry cycles increases by about 72.5% compared to the unmodified expansive soil. A higher amplitude of wet and dry cycles induces a faster decay of shear strength, resulting in smaller shear strength of 16.2 kPa for 8% cement-amended expansive soils at 4%→50% wet and dry amplitude than it at 4%→30% wet and dry amplitude at 100 kPa. Cement mainly increases the cohesion through cementation to enhance the strength of expansive soils, and as a result of the wet and dry cycle, the microscopic pores between the particles of the expanded soil are enlarged and the hydration products are partially dislodged, thus reducing its strength and consequently its shear strength.