Abstract: he effect of high-permeable distribution medium（DM）on resin flow behavior in the vacuum infusion molding process was studied through visualization flow experiments. The results show that DM is able to largely reduce the mold filling time in vacuum infusion molding process ， and mold filling time is linearly reduced with the scale of DM. The flow-enhancement effect of DM decreases with the thickness of fiber preforms. The difference of resin flow front between top and bottom of fiber preforms linearly increases with the thickness of fiber preforms. The flow-enhancement mechanism of DM takes markedly on thickness effect. This thickness effect is important for vacuum infusion molding processing parameter optimization and quality control.