Abstract: Internal erosion can lead to the simultaneous change of void ratio and fine content of sand, which affects its water retention property and unsaturated seepage. Four soil samples with different erosion degrees were collected, and four contrastive samples were prepared according to the corresponding void ratio or particle composition. Soil-Water Characteristic Curve tests including drying-wetting phase were carried out on the eight samples mentioned above, respectively, to reveal the effects of void ratio and fine content on water retention property and establish the predictive models considering the influence rules. The results show that with the increasing of the internal erosion degree, the fine particle content decreases from 35% to 22%, inducing an increase in the void ratio of nearly 60%. The combined influence of the above two factors causes a significant weakening of the water retention property of silty sand at the low suction stage below 50 kPa, and an increasing of the hysteretic degree in drying-wetting cycle, and the action effect of void ratio increasing is greater than that of fine particle content decreasing. Then combing the total amount of particle loss and the volumetric strain of seepage, the variation of void ratio is derived in the process of internal erosion, and the predictive model of Soil-Water Characteristic Curve is established considering two variables: void ratio and fine content, which could reflect the influence of different internal erosion degrees of silty sand.