In order to study the effects of root systems of herbs on unsaturated characteristics of the sandy soil, experiments were conducted to determine the soil-water characteristic indices of bare soil and vegetated soil around the root systems of three herbs(Cynodon dactylon, Festuca arundinace, and Vetiveria zizanioides)in the old course area of the Yellow River. Based on the soil-water characteristic curves fitted with the Brooks-Corey equation, functions of the pore radius change index and the unsaturated permeability coefficient were established. The results show that, compared with the bare soil, the air-entry value of the vegetated soil decreased, and the water-holding capacity increased. The average values of the soil pore radius of the vegetated sandy soil with Cynodon dactylon, Festuca arundinace, and Vetiveria zizanioides were 26 times, 12 times, and 59 times that of the bare soil, respectively. The permeability coefficients of the vegetated soil were two to three orders of magnitude higher than that of the bare soil with the same saturation within a range from 25% to 70%. The results show that the root systems of herbs formed aggregates in unsaturated sandy soil in the old course of the Yellow River.