Abstract: During the opening or closing of the downstream gate of trash rack, the trash rack will work at different flow Reynolds numbers, and its hydrodynamic characteristics are of great interest to researchers. To this end, the hydrodynamic characteristics of the trash rack at low and medium flow Reynolds numbers (Re≤3900) are investigated in detail. The Incompact3d open-source software framework with a high spatial and temporal resolution is used to solve the flow, and the fluid-solid boundary is dealt with using the immersed boundary method. The results show that the hydrodynamic characteristics of the trash rack at low and medium flow Reynolds numbers are closely related to the shedding of the leading-edge vortex and the generation of the trailing vortex, and the lift and drag coefficients show a periodic trend. As the Reynolds number increases, the time-averaged drag coefficient shows a trend of gradually decreasing, but the frequency of the drag and lift coefficient gradually increases. It is also found that the time-averaged drag coefficient shows a trend of gradually increase with the decrease of the fence spacing at Re≤3900, although the frequency of the drag and lift coefficient decreases gradually.