Rainfall is the main cause of landslides, the two are closely related. Based on the theory of saturatedunsaturated seepage and the theory of unsaturated soil shear strength, this paper makes an in-depth comparatve analysis on the infuence of short-term heavy rainfall and long-term weak rainfall on slope stability. The results show: The soil above the slope is more likely to reach saturaton under short-term heavy rainfall, while the infuence of long-term weak rainfall on the slope soil is deeper and the stability is greatly reduced. However, landslides with long periods of weak rainfall are more dangerous. In additon, the method of determining the critcal rainfall of a slope for landslide is obtained, and the safety status of the slope can be directly judged by comparing the actual rainfall with the critcal rainfall, and the classifcaton standard of the safety grade of a specifc slope is further obtained, which can provide reference for landslide preventon and treatment.