Abstract: Long-term rainfall causes progressive damage to a slope. In this process, the slip zone soil will reach the residual strength under different water-containing states with the change of water content. The traditional strain softening model cannot accurately express the dynamic characteristics of the residual strength of the slip zone soil during this change, resulting in difficulty to get close to reality in the simulation of the landslide development process. The strain softening model that involves the dynamic residual strength can more realistically simulate the development of the stability of the landslide when the water content changes. Based on this, the field investigation was carried out on the Kualiangzi landslide in Zhongjiang County in Sichuan, and the slip zone soil was obtained through the on-site shaft. The ring shear test is used to study the relationship between the mechanical parameters of the slip zone soil and the water content, and a strain softening model based on the dynamic residual strength is established to simulate the development of the Kualiangzi landslide when the slip zone soil is at different water content stages. The evolution process of the landslide through the evolution of the plastic zone and the sliding surface is analyzed and compared with the current failure characteristics. The research results show that the increase of water content makes the shear resistance of slip zone soil attenuate significantly, the peak and residual shear strength decrease almost linearly, and the residual strength parameters show the characteristics of cubic attenuation. The strain softening model established based on the attenuation law of residual strength parameters simulates the deformation and failure process of the Kualiangzi landslide. It is found that when the water content of the slip zone soil is less than 20%, the slope only produces a plastic zone at the front edge; when the water content reaches 22%, a plastic zone and a non-penetrated sliding surface begin to appear in the middle and upper parts of the slope; when the water content of the slip zone soil reaches 24%, the plastic zone tends to penetrate, the landslide enters a state of accelerated deformation, and tensile cracks are generated on the slope surface; when the water content reaches 26%, the landslide is in a state of instability, and the development of the tensile plastic zone and failure surface of the slope is highly consistent with the current failure characteristics of the landslide. The results can provide a certain theoretical basis for the stability study of related landslides.