The main reason of expansive soil embankment slope landslide is the infiltration of rainwater. Analyzing engineering characteristics and failure mechanism of expansive soil embankment slope, considering the force of expansion under the infiltration of rainwater, and choosing the appropriate constitutive model, simulate expansive soil embankment slope under humidification state. According different conditions of the expansive soil and different depth of infiltration, and simplifying the swelling force, establish a simple and reasonable model of expansion force changes. Expansive soil embankment slope stability is mainly affected by the moisture of expansive soil slope after analyzing the calculation results. The safety of expansive soil slope after immersion in rainwater decreases significantly. It shows designers should choose reasonable slope ratio and consider the embankment slope protection and drainage measures.