Rainfall is a primary factor inducing landslides on slopes, especially the slope repaired after in-situ leaching of ionic rare earth mine is more susceptible to rainfall infiltration. Taking the slope of an ionic rare earth mine in South China as the research background, the influences of rainfall, duration and rainfall type on slope stability was systematically analyzed based on the monitoring data of soil moisture and finite element simulation. The results show that the proportion of deep infiltration (deeper than 60 cm) events (accounting for 19.79%) of single-peak and multi-peak rainfall is significantly higher than that of concentrated (accounting for 1.04%) and uniform (accounting for 5.21%). The numerical simulation shows that the slope stability under the condition of low rainfall (10−20 mm/d) is concentrated>uniform>single peak>multi peak. The stability of single peak type is the worst when the rainfall is high (50 mm/d). With the increase of rainfall duration, the slope stability coefficient under concentrated and uniform rainfall conditions shows a trend of slow decline and then rapid decline, and the slope stability coefficient under single-peak and multi-peak rainfall conditions shows a trend of rapid decline and then slow decline, which is closely related to the sudden change of matrix suction caused by peak rainfall intensity. The research can provide a theoretical basis for the prevention and control of rainfall-induced landslides in ionic rare earth mines.