In this study, we have studied on the non linearity of hydraulic conductivity for Neogene sedimentary rocks under low hydraulic gradient. The behavior was tested not only by laboratory test but also in situ test taking account for accuracy under low hydralic condition. It's found that the non-Darcy is dominant in the hydraulic gradient less than 5 at the laboratory test. Also at the in situ test the non-Darcy behavior was found. We proposed the model of the flow under low hydraulic gradient using capillary model taking account of Bingham flow. This model is based on the assumption that the molecule of water is absorbed by the surface of micro condition. It was found that the non-Darcy behavior was well simulated when all capillary have a narrow (10^-8m) space.