Abstract: The research results regarding the threshold values for slope disasters caused by rainfall are crucial for geological disaster prevention. In this study, landslides induced by long-term heavy rainfall occurred in five counties within the Gansu section of the Bailongjiang Basin between 2004 and 2019. Using the frequency method, the rainfall thresholds for early warning of rainfall type landslides with different rock characteristics were investigated. A relationship model between event rainfall and the duration of rainfall leading to landslides was constructed under different probability levels, and a lower threshold for critical cumulative rainfall was provided. Through verification of landslide characteristics and rainfall data resulting from a flash flood disaster in Wudu District in 2020, the accumulated rainfall measured by the rainfall gauge before the landslide is found to be consistent with the threshold given by the model. This finding is of guiding significance for early warning of landslide disasters caused by sustained heavy rainfall.