Abstract: The contact scouring in the covering layer has attracted more and more concern in the engineering. The contact scouring at the interface between sandy gravel and cohesive soil is easy to happen, so it is necessary to study the main influence factors and the process of contact scouring to reveal its mechanism. Through the experiments of vertical and horizontal contact scouring, the influence of the dry density and grading of sandy gravel on the contact scouring between sandy gravel and cohesive soil is analyzed. The results show that the process of contact scouring can be divided into three stages, stable stage, transition stage and failure stage. The hydraulic gradient when the contact scouring just happens is called starting gradient, and it is called failure gradient when the seepage failure finally occurs. The contact scouring is mainly affected by the dry density and grading of sandy gravel. The greater the dry density of sandy gravel, the lower the permeability of the sample. At the same time, the starting gradient and the failure gradient both increase. The permeability is greater and the starting gradient and the failure gradient of contact scouring are lower when the particle of the sandy gravel becomes coarser. Compared with those under vertical contact scouring under the same condition, the permeability of samples under horizontal seepage is greater and the failure gradient is lower.