In recent years, drastic and extreme forms of soil erosion, such as landslides, mudflows, and silt dam outbursts, triggered by extreme rainstorms on the Loess Plateau have attracted widespread attention. From October 3 to 6, 2021, a large shallow landslide disaster was triggered by heavy rainfall along the Caijiachuan watershed in Jixian County, Shanxi Province. In this study, the rainfall process, landslide initiation conditions, and erosion characteristics were analyzed using predisaster and postdisaster unmanned aerial vehicle imagery, historical remote sensing images, and rainfall data provided by the National Field Scientific Observatory for Forest Ecosystems in Jixian County, Shanxi Province. The results show that it was a typical “long-duration, low-intensity” rainfall, with a total precipitation of 121.8 mm in the first 72 h of the initiation of the massive, shallow landslides and a rainfall intensity of 33.2 mm·(6h)^-1 during the initiation of the landslides. The landslide triggered by this rainstorm required a slightly smaller catchment area and exhibited higher landslide mobility than the landslide triggered by a typical short-duration, high-intensity rainstorm in 2003; however, the slope of the landslide was not significantly different. Thus, the cumulative rainfall in the early stage was the main factor influencing the occurrence and flexibility of the massive landslide disaster. The magnitude of landslide number probability, area probability, and erosion intensity in catchments with different land use types decreased in the following order: farmland catchment>plantation forest catchment>closed catchment. This finding indicated that the land use type and vegetation cover affect the degree of landslide erosion to a certain extent and that an arboreal-dominated watershed is more unfavorable to landslide initiation.