Abstract: Rainfall has a large effect on the stability of soil slopes. Under rainfall infiltration, the degree of saturation and water content of soil slope increase, and the matrix suction decreases. On the other hand, change of fluid pressure affects the deformation of soil skeleton. Based on the saturated-unsaturated seepage analysis and the strength reduction method, the coupled and uncoupled analysis of a soil slope under rainfall infiltration is analyzed. The influence of the coefficient of saturated hydraulic conductivity and the rainfall intensity on the slope stability is studied, and the relationship between the factor of safety and the position of sliding surface is obtained. This study illustrates that the saturated hydraulic conductivity has a large effect on slope stability. If the permeability of soils is relatively large, the changing range and velocity of the factor of safety increase with the rainfall intensity; and if it is relatively small, the influence of the rainfall intensity on the slope stability is also small. Under the same conditions, the factor of safety of uncoupled analysis is less than that of the coupled analysis. The position of the potential sliding surface varies with different rainfall intensities, e.g., the variation region of the sliding surface of uncoupled analysis occurs at the shoulder of the slope, while that of coupled analysis appears at the toe of the slope.