Abstract: The soil is a kind of special porous medium, whose internal pore channel is extremely random. As a result, the pore velocity distribution is not uniform in its seepage field, which is referred to the preference flow phenomenon. The preference flow is an important factor influencing the pollutant migration and infiltration deformation of the soil. Based on the principle of transparent soils, the saturated transparent porous medium is mixed with sodium polyacrylate cross-linked polymer particles and distilled water. A simple particle image velocimetry (PIV) system is combined with a green light laser, a SLR camera and a cross slide to study seepage in transparent medium. The flow field images of transparent porous medium under different hydraulic gradients are collected, and the velocity data obtained are statistically analyzed by combining with the particle image velocimetry technology to reveal the flow characteristics of pore fluid. The results show that the measured results are in good agreement with the macroscopic velocities. The simple PIV system can be used to measure the flow field with multi-point, non-interference and high precision. It is found that the pore area in the longitudinal section of porous medium is related to the location of the longitudinal section, and the larger the pore area, the larger the pore flow velocity on the section. The distribution of pore velocity in porous medium is approximately the same. With the decrease of longitudinal section velocity, the preference velocity decreases. The smaller the preference velocity is, the higher the probability density is, the more significant the preference flow phenomenon is.