Abstract: Contact erosion easily occurs at the interface between two soil layers subjected to a groundwater flow. Particles of the fine soils are eroded by the flow and transported through the pores of the coarse layer, which may lead to failure of a hydraulic structure. To investigate the meso-mechanism of contact erosion, different layers consisting of uniform particles subjected to a flow parallel to the interface are simulated using the particle flow code. The results show that when the ratio of the effective diameter of the fine layer to the effective pore diameter of the coarse layer is larger than 0.50, the contact erosion does not occur. When the contact erosion happens between layers, the fine particles at the interface will move and be transported by the flows. With the increase in the loss quantity of the fine particles, the coarse particles will sink and the flow velocity will increase.