Abstract: With the non-continuous and non-homogeneous features, gravel soil is a kind of structural material. Owing to the large number of rocks inside, it tends to form an overhead structure. Thus, the complex and unique seepage channels, i.e., the preferential flow paths come into being. The preferential flow paths of gravel soil are intricate which include moisture transport and migration of soil fine particles. The studies for the preferential flow path are apt to merely consider the moisture transport and ignore the migration of fine particles. However, particle migration is closely related to the path formation. This paper explored the spatial and temporal development rules from the perspective of fine particle migration through the experiments of saturated percolation-particle migration in two different gradation soil columns(continuous gradation and gaping gradation of rough particles and fine particles). The results show that: Part of the migratory fine particles cause erosion and increase the permeability, while others block local pores and reduce permeability owing to the re-deposited process. As a result, the formation of preferential flow is accelerated. In addition, the continuous grading forms the seepage paths with multiple intersecting tubuloreticular structures, while the gap gradating forms concentrated seepage paths. Moreover, under the same hydraulic gradient conditions, the distribution of fine particle migration in different grading features differently. The gravel soil fine particle migration does not change with the spatial distribution in the continuous grading but does change in the gap grading. In these two gradings, the main loss of gravel soil fine particles ranges from 1 mm to 0.075 mm in size. Under the different hydraulic gradient conditions, the loss of fine particles increases with the increase of hydraulic gradient in both continuous grading and gap grading experiments. Besides, the gap grading experiments are more prone to be damaged because the experiments show that when the gravel soil is damaged, the hydraulic gradient of gap grading is smaller than that of continuous grading. The results provide an experimental basis for further exploring the mechanism of gravel soil preferential flow formation.