Landslide is the common geological disaster in loess hilly and gully areas, and rainfall is the main cause of instability of loess slopes. In order to study the stability of loess slopes under continuous rainfall conditions, an artificial rainfall device was used to carry out experimental studies on the outdoor site. The soil moisture content, density, shear zone location and crack development were measured. The FLAC3D geotechnical engineering numerical calculation software was used to analyze the slope stability. The results showed that with the increase of rainfall duration, the moisture content of the loess slope soil gradually increased, the soil strength gradually decreased, and its own weight gradually increased. The gully erosion on the slope gradually developed, the slope toe collapsed, and the tensile cracks occurred on the top of the slope. The cracks increased the infiltration of rainfall, which made the strength of soil around the crack decrease rapidly, and finally caused a landslide when the rainfall lasted 308.8 h. Rainfall infiltration and concentrated infiltration caused by cracks accelerated the reduction of soil strength and led to the landslide. The deeper and more cracks developed, the greater their damage to slope stability.