The seepage caused by rainfall can reduce the stability of highway slopes, and then cause various slope disasters and affect the safe operation of highways. Therefore, it is particularly important to effectively ensure the stability of highway slope under precipitation conditions. The weathered rocky rainwater seepage slope of Yunmao expressway is taken as an example, numerical simulation methods are used to study the stability of the reinforced slope under different hydraulic gradients, and the change law of slope deformation and safety is revealed. The results show that: 1) The horizontal and vertical displacement of the slope increase with the increase of hydraulic gradient, and the displacement change of different positions is significantly affected by the hydraulic gradient; 2) The hydraulic gradient has a significant effect on the horizontal slip characteristics of the sliding surface; 3) The safety factor decreases exponentially with the increase of hydraulic gradient, and when the hydraulic gradient increases, the stability of the slope decreases sharply, and the risk of landslide disaster increases significantly. The results can be used as a reference for the design and stability prediction of seepage slope support.