Based on the rainfall profile in the landslide-prone area on the reservoir bank slope near the dam of the Longjiang Hydropower Plant in Yunnan Province, the slope stability under antecedent rainfall was investigated. By using the self-developed experimental apparatus, laboratory model tests were conducted to simulate landslides under antecedent rainfall, and the characteristics of landslides were analyzed. Research shows that antecedent rainfall is a major factor in landslides. Antecedent rainfall infiltrates the slope from the surface, reducing the soil strength and leading to a loss or reduction of the matrix suction in the unsaturated soil. Thus, the subsequent rainfall can easily generate landslides. Landslides induced by antecedent rainfall are categorized as shallow retrogressive landslides.