Abstract: Intense rainfall always results in the air in soil slopes being closed, and it will decrease the slope stability therefore. The present research mainly focuses on the effect of closed air pressure on infiltration and on the stability safety factor of an infinite soil slope when the slope slides along a plane located at wetting front surface. Firstly, based on the theory of closed air pressure and Green-Ampt model, a slope infiltration model which considers the effect of both air pressure and slope angleon infiltration was developed. Then, combining the Mohr-Coulomb failure criterion and the limit-equilibrium method, a model was established to calculate the stability safety factor (F_sa) of a infinite soil slope. The developed model is suitable for evaluating the F_sa when the slope slides along the plane located under phreatic surface since this model can consider the decreasing effect of closed air pressure on the effective stress of soil under phreatic surface. Finally, the influences of air pressure on infinite soil slope, as well as the variation of F_sa when the slope slides along different planes, were studied. The results indicate that air pressure significantly reduces the slope stability, and the smaller the c' is, the larger the ϕ' is, the smaller the slope angle is, and the shallower the sliding surface is, the more the air pressure affects F_sa. It also shows that the critical sliding surface may locate under the phreatic surface.