[Objective] The depth of rainfall infiltration in loess region was analyzed in order to provide the basis for studying the mechanism of loess landslide.[Methods] The variations of soil water content at different depths were monitored by field observation, and the numerical simulation of rainfall infiltration process was carried out based on the particle discrete element method.[Results] The monitoring results showed that the depth of rainfall infiltration in loess area was less than 1.5 m. Numerical calculation found that the dominant channel infiltration depth is related to the geometry of the cracks, the deeper or the wider of the cracks, the deeper and wider of the rainfall infiltration. Besides, the cracks had different geometry characteristics in the process of rainfall infiltration.[Conclusion] The rainfall infiltration in loess can be divided into 2 types:unsaturated infiltration and dominant channel infiltration. The depth of unsaturated infiltration is limited, but the penetration depth of the dominant channel is comparatively larger that can potentially induce large-scale landslide disaster.