Abstract: Regional preferential passages are developed in loess area, which have changed the runoff and infiltration process of rainfall and irrigation water, reduced the soil strength, and caused geological disasters such as slope instability and collapse and landslide. After studying the trailing edge and landslide body of DH2^# in Heifangtai, the physical characteristics of preferential passage have been summarized in this paper, and the non-invasive research method has been used to study the effectiveness of the preferential passage refinement detection method based on geophysical method. Based on the intervention of artificial watering and flooding, the high-density resistivity (0.20m) and ground penetrating radar (0.02m) with small distance has been used to identify the development and distribution characteristics of micro-cracks (width 0.2-0.5m),cracks in the trailing edge of the landslide and the sliding surface. And the fine detection of preferential passage such as the micro-crack of the loess has been realized, which proves the effectiveness of fine geophysical application. At the same time, under the combined effects from the infiltration and erosion of irrigation water and the creep and sliding of loess, the micro-cracks gradually develop into cracks, which form the transformation relationship of sliding surface, and provide research basis for the loess preferential flow and landslide study. This technology has great application prospects in urban geological problems, such as ground fissures and micro-fracture detection in the loess area.