Abstract:In order to explore the seepage characteristics in loess, and clarify the influence extent of different initial conditions on preferential flow, a dye tracing experiment was carried out in the southern Loess Plateau, using brilliant blue and ionic dye and controlling the infiltration water and initial water content. According to the obtained dyeing image, the preferential flow extent was analyzed qualitatively and quantitatively. The results showed that the dyeing depth of brilliant blue in loess was limited, while the ionic dye could well trace the seepage of water after color reaction. The type of preferential flow in loess in southern Loess Plateau from small to large with depth was in order as follows: homogeneous matrix flow, heterogeneous matrix flow and fingering, macropore flow with high interaction, macropore flow with mixed interaction. The order of preferential flow indicator was test pit A (0.55)>test pit C (0.48) >test pit B (0.46), and the extent of preferential flow was from high to low: test pit A, test pit C, test pit B. When other conditions were the same, more infiltration water and higher initial water content in loess would inhibit the development of preferential flow, resulting in greater depth of matrix infiltration, higher extent of matrix flow, and lower extent of preferential flow. The study can provide reference for disaster prevention and control in loess area and for proving the mechanism of groundwater pollution.