Expansive soil is susceptible to the influence of water content, and the atmospheric environment can induce the dry-wet cycle, posing a significant threat to the stability of the expansive soil slope. In this study, a set of dry-wet cycle tests was designed to simulate the effect of the atmospheric environment, and the effect of different numbers of dry-wet cycles on the shear strength of expansive soil was investigated through direct shear tests. Based on the test results, the influence of the dry-wet cycle on the stability of expansive soil slopes was analyzed using the finite element method. The results show that the dry-wet cycle has a significant effect on the shear strength of expansive soil, mainly manifested in a significant decrease in cohesion, while the change in internal friction angle is not significant, and the dry-wet cycle effect is mainly reflected in the first dry-wet cycle process. The essence of the significant deterioration of expansive soil strength is that the structure of expansive soil is significantly destroyed under the condition of a dry-wet cycle, resulting in a large number of cracks in the soil. Under the influence of the dry-wet cycle, the failure mode of expansive soil slopes is mainly a shallow failure, and the stability factor of the slope first sharply decreases and then decays slightly. The influence mechanism of the dry-wet cycle on the stability of expansive soil slope includes two aspects: a shallow atmospheric influence layer and a significant reduction of strength parameters. It is recommended to fully avoid the dry-wet cycle effect when protecting expansive soil slopes from failure, and laying cushions and planting grass on slopes are valuable methods.