Abstract: In order to study the influence of upward seepage on the flow characteristics around uniform coarse grains, we experimentally measured the flow structures around uniform coarse grains under the impact of upward seepage by the technique of Particle Image Velocimetry (PIV), we subsequently analyzed the two-dimensional vertical flow structure around the particle group with different relative upward seepage intensities. The results show that upward seepage decreases the velocity along the mainstream direction and increases the vertical upward velocity around the particle group. With the relative upward seepage intensity increases, both of them become more affected. We also proposed an empirical formula for the longitudinal current velocity distribution under the impact of upward seepage based on the measurements. We finally found that the upward seepage could enhance the turbulence intensity and energy dissipation around the particle group, and the value of vorticity around uniform coarse grains decreases with the increase of relative upward seepage intensity.