Disturbance and rainfall are important factors affecting the stability of the slope, which seriously endangers the safety of the project. Taking a highway mixed granite cutting slope as an example, the soil layer structure information of the mixed granite slope was obtained by means of geophysical methods such as electrical measurement. On this basis, a numerical model is established to calculate the slope stability under excavation, rainfall and other disturbance conditions, and the safety stability coefficient of the slope under different working conditions is obtained. The results show that the overall stability of the mixed granite cutting slope is high under the excavation of engineering excavation. The stability coefficient of slope is Fs = 1.41, and there is almost no plastic strain on the slope. Under the condition of rainy season, the side Plastic strain occurs on the surface of the slope, and the mixed granite is softened by the influence of rainwater. The stability coefficient of the slope is Fs = 0.86, which is easy to cause surface damage. In the case of protective reinforcement, most of the time it is necessary to consider the erosion of the slope surface; at the same time there is a slope of the fault, in addition to the reinforcement of the slope surface, the slope must be deepened. The research results have guiding significance for the safe construction of mixed granite cutting slope.