This paper propose a slope stability analysis method based on the fluid solid coupling theory and the sensitivity analysis of unsaturated seepage parameters for study the slope stability under the condition of rainfall infiltration. The interaction of unsaturated parameters affects the slope stability, therefore, the slope stability analysis model of unsaturated seepage based on the finite element method is established. The sensitivity analysis model of slope stability analysis parameters is established, and the direct and coupling interaction of unsaturated parameters on slope stability characteristics are analyzed. The results showed that the direct and interaction influence of rainfall intensity and permeability coefficient on the pore pressure and saturation characteristics of slope stability is more obvious than that of internal friction angle and cohesion under the under the interaction of unsaturated parameters during rainfall infiltration. The displacement of the feature element is extremely affected by rainfall intensity, and the interaction effect of the internal friction angle and other parameters is the most significant. The cohesion has the most direct influence on the stability of the slope, and it is most closely related to the angle of internal friction, rainfall intensity and saturated permeability coefficient that affect the plastic deformation. The interaction effect is not the direct superposition of single parameters when the unsaturated parameters changes synchronously.