Abstract: Non-darcy seepage through layered porous media is common in soil-groundwater systems under the influence of human activities. The effect of average particle size and coarse-fine particle interface on the characteristics of non-Darcy porous flow through layered porous media was investigated from the relation between hydraulic gradient and flow velocity, non-Darcy seepage parameters, and critical Reynolds number. The results show that when water flows through layered porous media, the coarse-fine particle interface has an important effect on the characteristics of non-Darcy flow. The critical Reynolds number, which is used to judge the transition from Darcy flow to non-Darcy flow, decreases with the increase of the average particle size in monolayer porous media, but increases with the increase of the average particle size and the decrease of the coarse/fine particle size ratio when water flows through layered porous media. The critical Reynolds number of single-layer porous media is lower than that of the double-layer porous media with the same corresponding particle size due to the coarse-fine particle interface. By introducing the nonlinear component index E, it is found that the coarse/fine particle interface has a certain inhibitory effect on the hydrodynamic inertia force component, and the inhibitory effect degree is negatively correlated with the difference in size of the coarse and fine particles. The results in this study have a good guiding significance for studying non-Darcy seepage through layered rock and soil.